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libata: add comment documenting PIO latency issues on UP

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Based on:
http://lkml.indiana.edu/hypermail/linux/kernel/0908.2/01420.html

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
This commit is contained in:
Bartlomiej Zolnierkiewicz 2009-11-26 17:11:16 +01:00 committed by Jeff Garzik
parent 5600c70e57
commit 9cd13bdbae
1 changed files with 7 additions and 0 deletions
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7
drivers/ata/libata-core.c
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@ -6616,6 +6616,13 @@ static int __init ata_init(void)
{ {
ata_parse_force_param(); ata_parse_force_param();
/*
* FIXME: In UP case, there is only one workqueue thread and if you
* have more than one PIO device, latency is bloody awful, with
* occasional multi-second "hiccups" as one PIO device waits for
* another. It's an ugly wart that users DO occasionally complain
* about; luckily most users have at most one PIO polled device.
*/
ata_wq = create_workqueue("ata"); ata_wq = create_workqueue("ata");
if (!ata_wq) if (!ata_wq)
goto free_force_tbl; goto free_force_tbl;