2013-10-14 12:58:56

by Dorau, Lukasz

[permalink] [raw]
Subject: [PATCH] libahci: fix turning on LEDs in ahci_start_port()

If EM Transmit bit is busy during init ata_msleep() is called.
It is wrong - msleep() should be used instead of ata_msleep(),
because if EM Transmit bit is busy for one port, it will be busy
for all other ports too, so using ata_msleep() causes wasting
tries for another ports.

The most common scenario looks like that now
(six ports try to transmit a LED meaasege):
- port #0 tries for the 1st time and succeeds
- ports #1-5 try for the 1st time and sleeps
- port #1 tries for the 2nd time and succeeds
- ports #2-5 try for the 2nd time and sleeps
- port #2 tries for the 3rd time and succeeds
- ports #3-5 try for the 3rd time and sleeps
- port #3 tries for the 4th time and succeeds
- ports #4-5 try for the 4th time and sleeps
- port #4 tries for the 5th time and succeeds
- port #5 tries for the 5th time and sleeps
At this moment port #5 wasted all its five tries and failed to initialize.
Because there are only 5 (EM_MAX_RETRY) tries available usually only five ports
succeed to initialize. The sixth port and next ones usually will fail.

If msleep() is used instead of ata_msleep() the first port succeeds to initialize
in the first try and next ones usually succeed to initialize in the second try.

Signed-off-by: Lukasz Dorau <[email protected]>
---
drivers/ata/libahci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index acfd0f7..cf38692 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -779,7 +779,7 @@ static void ahci_start_port(struct ata_port *ap)
emp->led_state,
4);
if (rc == -EBUSY)
- ata_msleep(ap, 1);
+ msleep(1);
else
break;
}


2013-10-14 13:20:55

by Tejun Heo

[permalink] [raw]
Subject: Re: [PATCH] libahci: fix turning on LEDs in ahci_start_port()

On Mon, Oct 14, 2013 at 02:58:19PM +0200, Lukasz Dorau wrote:
> If EM Transmit bit is busy during init ata_msleep() is called.
> It is wrong - msleep() should be used instead of ata_msleep(),
> because if EM Transmit bit is busy for one port, it will be busy
> for all other ports too, so using ata_msleep() causes wasting
> tries for another ports.
>
> The most common scenario looks like that now
> (six ports try to transmit a LED meaasege):
> - port #0 tries for the 1st time and succeeds
> - ports #1-5 try for the 1st time and sleeps
> - port #1 tries for the 2nd time and succeeds
> - ports #2-5 try for the 2nd time and sleeps
> - port #2 tries for the 3rd time and succeeds
> - ports #3-5 try for the 3rd time and sleeps
> - port #3 tries for the 4th time and succeeds
> - ports #4-5 try for the 4th time and sleeps
> - port #4 tries for the 5th time and succeeds
> - port #5 tries for the 5th time and sleeps
> At this moment port #5 wasted all its five tries and failed to initialize.
> Because there are only 5 (EM_MAX_RETRY) tries available usually only five ports
> succeed to initialize. The sixth port and next ones usually will fail.
>
> If msleep() is used instead of ata_msleep() the first port succeeds to initialize
> in the first try and next ones usually succeed to initialize in the second try.

Ah, interesting.

> Signed-off-by: Lukasz Dorau <[email protected]>
> ---
> drivers/ata/libahci.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
> index acfd0f7..cf38692 100644
> --- a/drivers/ata/libahci.c
> +++ b/drivers/ata/libahci.c
> @@ -779,7 +779,7 @@ static void ahci_start_port(struct ata_port *ap)
> emp->led_state,
> 4);
> if (rc == -EBUSY)
> - ata_msleep(ap, 1);
> + msleep(1);

This is so unobvious. Can you please add a comment explaining what's
going on?

Thanks.

--
tejun

2013-10-14 16:17:32

by Dorau, Lukasz

[permalink] [raw]
Subject: RE: [PATCH] libahci: fix turning on LEDs in ahci_start_port()

On Monday, October 14, 2013 3:21 PM Tejun Heo <[email protected]> wrote:
> On Mon, Oct 14, 2013 at 02:58:19PM +0200, Lukasz Dorau wrote:
> > If EM Transmit bit is busy during init ata_msleep() is called.
> > It is wrong - msleep() should be used instead of ata_msleep(), because
> > if EM Transmit bit is busy for one port, it will be busy for all other
> > ports too, so using ata_msleep() causes wasting tries for another
> > ports.
> >
> > The most common scenario looks like that now (six ports try to
> > transmit a LED meaasege):
> > - port #0 tries for the 1st time and succeeds
> > - ports #1-5 try for the 1st time and sleeps
> > - port #1 tries for the 2nd time and succeeds
> > - ports #2-5 try for the 2nd time and sleeps
> > - port #2 tries for the 3rd time and succeeds
> > - ports #3-5 try for the 3rd time and sleeps
> > - port #3 tries for the 4th time and succeeds
> > - ports #4-5 try for the 4th time and sleeps
> > - port #4 tries for the 5th time and succeeds
> > - port #5 tries for the 5th time and sleeps At this moment port #5
> > wasted all its five tries and failed to initialize.
> > Because there are only 5 (EM_MAX_RETRY) tries available usually only
> > five ports succeed to initialize. The sixth port and next ones usually will fail.
> >
> > If msleep() is used instead of ata_msleep() the first port succeeds to
> > initialize in the first try and next ones usually succeed to initialize in the second
> try.
>
> Ah, interesting.
>
> > Signed-off-by: Lukasz Dorau <[email protected]>
> > ---
> > drivers/ata/libahci.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c index
> > acfd0f7..cf38692 100644
> > --- a/drivers/ata/libahci.c
> > +++ b/drivers/ata/libahci.c
> > @@ -779,7 +779,7 @@ static void ahci_start_port(struct ata_port *ap)
> > emp->led_state,
> > 4);
> > if (rc == -EBUSY)
> > - ata_msleep(ap, 1);
> > + msleep(1);
>
> This is so unobvious. Can you please add a comment explaining what's going
> on?
>

OK, I will send the second version of the patch soon.

Thanks,
Lukasz