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

On Fri, 6 Mar 2009, Jens Axboe wrote:

On Thu, Mar 05 2009, Geert Uytterhoeven wrote:

quoted

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

Sony Techsoft Centre Europe
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