linux-kernel - Re: SATA resume slowness, e1000 MSI warning

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Message-ID: <45EEE8CF.1060803@intel.com>
Date:	Wed, 07 Mar 2007 08:31:11 -0800
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	"Kok, Auke" <auke-jan.h.kok@...el.com>,
	Ingo Molnar <mingo@...e.hu>, Jeff Garzik <jeff@...zik.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Michael S. Tsirkin" <mst@...lanox.co.il>,
	Pavel Machek <pavel@....cz>,
	Jens Axboe <jens.axboe@...cle.com>,
	Adrian Bunk <bunk@...sta.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, linux-pm@...ts.osdl.org,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>
Subject: Re: SATA resume slowness, e1000 MSI warning

Eric W. Biederman wrote:
> "Kok, Auke" <auke-jan.h.kok@...el.com> writes:
> 
>> Ingo Molnar wrote:
>>> * Kok, Auke <auke-jan.h.kok@...el.com> wrote:
>>>
>>>>>> BUG: at drivers/pci/msi.c:611 pci_enable_msi()
>>>>> I would poke Eric Biederman(sp?) about this one.  Maybe its even solved by
>>>>> the MSI-enable-related patch he posted in the past 24-48 hours.
>>>> I tried the 3-patch series "[PATCH 0/3] Basic msi bug fixes.." and they fix
>>>> this problem for me. Were you expecting the OOPS in the first place? [...]
>>> the bug was the warning message (a WARN_ON()) above - not an oops. So that
>>> warning message is gone in your testing?
>> yes.
> 
> Sorry for the slow delay.  I was out of town for my brothers wedding the last few
> days.
> 
> I wasn't exactly expecting the WARN_ON to trigger.  What I fixed was
> an inconsistency in handling our state bits.  Fixing that
> inconsistency appears to have fixed the e1000 usage scenario mostly by
> accident.
> 
> The basic issue is that pci_save_state saves the current msi state
> along with other registers, and then the e1000 driver goes and
> disables the msi irq after we have saved the irq state as on.
> 
> My code notices that the msi irq was disabled before restore time, so
> it skips the restore.  However we now have a leak of the msi saved cap
> because we are not freeing it. 
> 
> This leaves with some basic questions.
> - Does it make sense for suspend/resume methods to request/free irqs?
> - Does it make sense for suspend/resume methods to allocate/free msi irqs?
> - Do we want pci_save/restore_cap to save/restore msi state?
> 
> The path of least resistance is to just free the extra state and we
> are good.  I'm just not quite certain that is sane and it has been a
> long day.

we used to have a lengthy e1000_pci_save|restore_state in our code, which is now 
gone, so I'm all for that. A separate pci_save_pxie|msi(x)_state for every 
driver seems completely unnecessary. I can't think of a use case where 
saving+restoring everything hurts. That's what you want I presume.

We currently free all irq's and msi before going into suspend in e1000, and I 
think that is probably a good thing, somehow I can think of bad things happening 
if we dont, but I admit that I haven't tried it without alloc/free. We do this 
in e100 as well and it works.

Another motivation would be to leave this up to the driver: if the driver 
chooses to free/alloc interrupts because it makes sense, you probably would want 
to keep that choice available. Devices that don't need this can skip the 
alloc/free, but leave the choice open for others.

hth

Auke
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