[Cbe-oss-dev] [PATCH/RFC] ps3/block: Add ps3vram-ng driver for accessing video RAM as block device

[Geert Uytterhoeven]

On Fri, 6 Mar 2009, Jens Axboe wrote:
> On Thu, Mar 05 2009, Geert Uytterhoeven wrote:
> > But then I noticed ps3vram_make_request() may be called concurrently,
> > so I had to add a mutex to avoid data corruption. This slows the
> > driver down, and in the end, the version with a thread turns out to be
> > ca. 1% faster. The version without a thread is about 50 lines less
> > code, though.
> 
> That is correct, ->make_request_fn may get reentered. I'm not surprised
> that performance dropped if you just shoved everything under a mutex.
> You could be a little more smart and queue concurrent bio's for
> processing when the current one is complete though, there are several
> approaches there that be a lot faster than going all the way through the
> IO stack and scheduler just to avoid concurrency.

Yes, using a spinlock and queueing requests on a list if the driver is busy can
be done after 2.6.29...

With kind regards,

Geert Uytterhoeven
Software Architect

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