mmcqd cpu utilization

mmcqd cpu utilization

[Madhusudhan]

Hi,

Has anyone monitored the cpu utilization percentage when a MMC/SD card is in
use? I have noticed that mmc_queue_thread "mmcqd" consumes a lot of cpu
cycles in a periodic fashion. What I mean here is that I see spikes of high
cpu utilization due to mmcqd. There will a cp or similar which will be
already consuming cpu to transfer data to the MMC/SD device. Further mmcqd
increases that load randomly to a high number.

Has anyone seen similar behavior? Any thoughts?

Regards,
Madhu  

Re: mmcqd cpu utilization

[Pierre Ossman]

[-- Attachment #1: Type: text/plain, Size: 1008 bytes --]

On Wed, 2 Sep 2009 12:23:59 -0500
"Madhusudhan" <madhu.cr@ti.com> wrote:

> Hi,
> 
> Has anyone monitored the cpu utilization percentage when a MMC/SD card is in
> use? I have noticed that mmc_queue_thread "mmcqd" consumes a lot of cpu
> cycles in a periodic fashion. What I mean here is that I see spikes of high
> cpu utilization due to mmcqd. There will a cp or similar which will be
> already consuming cpu to transfer data to the MMC/SD device. Further mmcqd
> increases that load randomly to a high number.
> 
> Has anyone seen similar behavior? Any thoughts?
> 

My guess would be that the omap driver doesn't (cannot?) use the
hardware to wait for busy to end, so the system must poll.

Anything better than that guess will require some profiling. :)

Rgds
-- 
     -- Pierre Ossman

  WARNING: This correspondence is being monitored by the
  Swedish government. Make sure your server uses encryption
  for SMTP traffic and consider using PGP for end-to-end
  encryption.

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 198 bytes --]

RE: mmcqd cpu utilization

[Madhusudhan]

> -----Original Message-----
> From: Pierre Ossman [mailto:pierre@ossman.eu]
> Sent: Wednesday, September 02, 2009 12:41 PM
> To: Madhusudhan
> Cc: linux-mmc@vger.kernel.org; linux-omap@vger.kernel.org; hch@lst.de
> Subject: Re: mmcqd cpu utilization
> 
> On Wed, 2 Sep 2009 12:23:59 -0500
> "Madhusudhan" <madhu.cr@ti.com> wrote:
> 
> > Hi,
> >
> > Has anyone monitored the cpu utilization percentage when a MMC/SD card
> is in
> > use? I have noticed that mmc_queue_thread "mmcqd" consumes a lot of cpu
> > cycles in a periodic fashion. What I mean here is that I see spikes of
> high
> > cpu utilization due to mmcqd. There will a cp or similar which will be
> > already consuming cpu to transfer data to the MMC/SD device. Further
> mmcqd
> > increases that load randomly to a high number.
> >
> > Has anyone seen similar behavior? Any thoughts?
> >
> 
> My guess would be that the omap driver doesn't (cannot?) use the
> hardware to wait for busy to end, so the system must poll.
> 
So your guess hints probably at "wait_for_completion(&complete)".
Am I correct?

Regards,
Madhu

> Anything better than that guess will require some profiling. :)
> 
> Rgds
> --
>      -- Pierre Ossman
> 
>   WARNING: This correspondence is being monitored by the
>   Swedish government. Make sure your server uses encryption
>   for SMTP traffic and consider using PGP for end-to-end
>   encryption.

RE: mmcqd cpu utilization

[Dasgupta, Romit]

Madhu,
>
>> My guess would be that the omap driver doesn't (cannot?) use the
>> hardware to wait for busy to end, so the system must poll.
>>
>So your guess hints probably at "wait_for_completion(&complete)".
>Am I correct?
>
Madhu wait_for_completion is blocking call. Please check 'omap_mmc_request'