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[PATCH] pipe: enable atomic copying of pipe data to/from user space
The pipe ->map() method uses kmap() to virtually map the pages, which is both slow and has known scalability issues on SMP. This patch enables atomic copying of pipe pages, by pre-faulting data and using kmap_atomic() instead. lmbench bw_pipe and lat_pipe measurements agree this is a Good Thing. Here are results from that on a UP machine with highmem (1.5GiB of RAM), running first a UP kernel, SMP kernel, and SMP kernel patched. Vanilla-UP: Pipe bandwidth: 1622.28 MB/sec Pipe bandwidth: 1610.59 MB/sec Pipe bandwidth: 1608.30 MB/sec Pipe latency: 7.3275 microseconds Pipe latency: 7.2995 microseconds Pipe latency: 7.3097 microseconds Vanilla-SMP: Pipe bandwidth: 1382.19 MB/sec Pipe bandwidth: 1317.27 MB/sec Pipe bandwidth: 1355.61 MB/sec Pipe latency: 9.6402 microseconds Pipe latency: 9.6696 microseconds Pipe latency: 9.6153 microseconds Patched-SMP: Pipe bandwidth: 1578.70 MB/sec Pipe bandwidth: 1579.95 MB/sec Pipe bandwidth: 1578.63 MB/sec Pipe latency: 9.1654 microseconds Pipe latency: 9.2266 microseconds Pipe latency: 9.1527 microseconds Signed-off-by: Jens Axboe <axboe@suse.de>
This commit is contained in:
Jens Axboe
parent
e27dedd84c
commit
f6762b7ad8
3 changed files with 126 additions and 30 deletions
129
fs/pipe.c
129
fs/pipe.c
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@ -55,7 +55,8 @@ void pipe_wait(struct pipe_inode_info *pipe)
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}
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static int
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pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len)
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pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len,
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int atomic)
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{
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unsigned long copy;
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@ -64,8 +65,13 @@ pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len)
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iov++;
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copy = min_t(unsigned long, len, iov->iov_len);
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if (atomic) {
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if (__copy_from_user_inatomic(to, iov->iov_base, copy))
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return -EFAULT;
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} else {
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if (copy_from_user(to, iov->iov_base, copy))
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return -EFAULT;
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}
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to += copy;
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len -= copy;
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iov->iov_base += copy;
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@ -75,7 +81,8 @@ pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len)
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}
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static int
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pipe_iov_copy_to_user(struct iovec *iov, const void *from, unsigned long len)
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pipe_iov_copy_to_user(struct iovec *iov, const void *from, unsigned long len,
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int atomic)
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{
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unsigned long copy;
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@ -84,8 +91,13 @@ pipe_iov_copy_to_user(struct iovec *iov, const void *from, unsigned long len)
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iov++;
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copy = min_t(unsigned long, len, iov->iov_len);
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if (atomic) {
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if (__copy_to_user_inatomic(iov->iov_base, from, copy))
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return -EFAULT;
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} else {
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if (copy_to_user(iov->iov_base, from, copy))
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return -EFAULT;
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}
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from += copy;
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len -= copy;
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iov->iov_base += copy;
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@ -94,6 +106,47 @@ pipe_iov_copy_to_user(struct iovec *iov, const void *from, unsigned long len)
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return 0;
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}
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/*
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* Attempt to pre-fault in the user memory, so we can use atomic copies.
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* Returns the number of bytes not faulted in.
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*/
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static int iov_fault_in_pages_write(struct iovec *iov, unsigned long len)
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{
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while (!iov->iov_len)
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iov++;
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while (len > 0) {
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unsigned long this_len;
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this_len = min_t(unsigned long, len, iov->iov_len);
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if (fault_in_pages_writeable(iov->iov_base, this_len))
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break;
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len -= this_len;
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iov++;
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}
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return len;
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}
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/*
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* Pre-fault in the user memory, so we can use atomic copies.
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*/
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static void iov_fault_in_pages_read(struct iovec *iov, unsigned long len)
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{
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while (!iov->iov_len)
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iov++;
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while (len > 0) {
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unsigned long this_len;
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this_len = min_t(unsigned long, len, iov->iov_len);
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fault_in_pages_readable(iov->iov_base, this_len);
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len -= this_len;
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iov++;
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}
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}
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static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
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struct pipe_buffer *buf)
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{
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@ -111,14 +164,23 @@ static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
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}
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void *generic_pipe_buf_map(struct pipe_inode_info *pipe,
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struct pipe_buffer *buf)
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struct pipe_buffer *buf, int atomic)
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{
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if (atomic) {
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buf->flags |= PIPE_BUF_FLAG_ATOMIC;
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return kmap_atomic(buf->page, KM_USER0);
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}
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return kmap(buf->page);
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}
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void generic_pipe_buf_unmap(struct pipe_inode_info *pipe,
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struct pipe_buffer *buf)
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struct pipe_buffer *buf, void *map_data)
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{
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if (buf->flags & PIPE_BUF_FLAG_ATOMIC) {
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buf->flags &= ~PIPE_BUF_FLAG_ATOMIC;
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kunmap_atomic(map_data, KM_USER0);
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} else
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kunmap(buf->page);
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}
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@ -183,7 +245,7 @@ pipe_readv(struct file *filp, const struct iovec *_iov,
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struct pipe_buf_operations *ops = buf->ops;
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void *addr;
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size_t chars = buf->len;
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int error;
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int error, atomic;
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if (chars > total_len)
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chars = total_len;
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@ -195,12 +257,21 @@ pipe_readv(struct file *filp, const struct iovec *_iov,
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break;
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}
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addr = ops->map(pipe, buf);
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error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars);
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ops->unmap(pipe, buf);
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atomic = !iov_fault_in_pages_write(iov, chars);
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redo:
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addr = ops->map(pipe, buf, atomic);
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error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars, atomic);
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ops->unmap(pipe, buf, addr);
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if (unlikely(error)) {
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/*
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* Just retry with the slow path if we failed.
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*/
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if (atomic) {
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atomic = 0;
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goto redo;
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}
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if (!ret)
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ret = -EFAULT;
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ret = error;
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break;
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}
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ret += chars;
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@ -304,21 +375,28 @@ pipe_writev(struct file *filp, const struct iovec *_iov,
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int offset = buf->offset + buf->len;
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if (ops->can_merge && offset + chars <= PAGE_SIZE) {
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int error, atomic = 1;
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void *addr;
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int error;
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error = ops->pin(pipe, buf);
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if (error)
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goto out;
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addr = ops->map(pipe, buf);
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iov_fault_in_pages_read(iov, chars);
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redo1:
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addr = ops->map(pipe, buf, atomic);
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error = pipe_iov_copy_from_user(offset + addr, iov,
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chars);
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ops->unmap(pipe, buf);
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chars, atomic);
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ops->unmap(pipe, buf, addr);
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ret = error;
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do_wakeup = 1;
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if (error)
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if (error) {
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if (atomic) {
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atomic = 0;
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goto redo1;
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}
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goto out;
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}
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buf->len += chars;
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total_len -= chars;
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ret = chars;
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@ -341,7 +419,8 @@ pipe_writev(struct file *filp, const struct iovec *_iov,
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int newbuf = (pipe->curbuf + bufs) & (PIPE_BUFFERS-1);
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struct pipe_buffer *buf = pipe->bufs + newbuf;
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struct page *page = pipe->tmp_page;
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int error;
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char *src;
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int error, atomic = 1;
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if (!page) {
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page = alloc_page(GFP_HIGHUSER);
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@ -361,11 +440,27 @@ pipe_writev(struct file *filp, const struct iovec *_iov,
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if (chars > total_len)
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chars = total_len;
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error = pipe_iov_copy_from_user(kmap(page), iov, chars);
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iov_fault_in_pages_read(iov, chars);
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redo2:
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if (atomic)
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src = kmap_atomic(page, KM_USER0);
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else
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src = kmap(page);
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error = pipe_iov_copy_from_user(src, iov, chars,
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atomic);
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if (atomic)
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kunmap_atomic(src, KM_USER0);
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else
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kunmap(page);
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if (unlikely(error)) {
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if (atomic) {
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atomic = 0;
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goto redo2;
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}
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if (!ret)
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ret = -EFAULT;
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ret = error;
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break;
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}
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ret += chars;
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@ -640,13 +640,13 @@ find_page:
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/*
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* Careful, ->map() uses KM_USER0!
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*/
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char *src = buf->ops->map(info, buf);
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char *src = buf->ops->map(info, buf, 1);
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char *dst = kmap_atomic(page, KM_USER1);
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memcpy(dst + offset, src + buf->offset, this_len);
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flush_dcache_page(page);
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kunmap_atomic(dst, KM_USER1);
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buf->ops->unmap(info, buf);
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buf->ops->unmap(info, buf, src);
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}
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ret = mapping->a_ops->commit_write(file, page, offset, offset+this_len);
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@ -5,7 +5,8 @@
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#define PIPE_BUFFERS (16)
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#define PIPE_BUF_FLAG_LRU 0x01
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#define PIPE_BUF_FLAG_LRU 0x01 /* page is on the LRU */
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#define PIPE_BUF_FLAG_ATOMIC 0x02 /* was atomically mapped */
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struct pipe_buffer {
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struct page *page;
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@ -28,8 +29,8 @@ struct pipe_buffer {
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*/
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struct pipe_buf_operations {
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int can_merge;
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void * (*map)(struct pipe_inode_info *, struct pipe_buffer *);
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void (*unmap)(struct pipe_inode_info *, struct pipe_buffer *);
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void * (*map)(struct pipe_inode_info *, struct pipe_buffer *, int);
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void (*unmap)(struct pipe_inode_info *, struct pipe_buffer *, void *);
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int (*pin)(struct pipe_inode_info *, struct pipe_buffer *);
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void (*release)(struct pipe_inode_info *, struct pipe_buffer *);
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int (*steal)(struct pipe_inode_info *, struct pipe_buffer *);
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@ -64,8 +65,8 @@ void free_pipe_info(struct inode * inode);
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void __free_pipe_info(struct pipe_inode_info *);
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/* Generic pipe buffer ops functions */
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void *generic_pipe_buf_map(struct pipe_inode_info *, struct pipe_buffer *);
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void generic_pipe_buf_unmap(struct pipe_inode_info *, struct pipe_buffer *);
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void *generic_pipe_buf_map(struct pipe_inode_info *, struct pipe_buffer *, int);
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void generic_pipe_buf_unmap(struct pipe_inode_info *, struct pipe_buffer *, void *);
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void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
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int generic_pipe_buf_pin(struct pipe_inode_info *, struct pipe_buffer *);
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