libata: add comment documenting PIO latency issues on UP

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

View file

@ -6616,6 +6616,13 @@ static int __init ata_init(void)
{
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");
if (!ata_wq)
goto free_force_tbl;