Messages in this thread | | | Date | Mon, 9 Mar 2009 11:52:12 +0100 (CET) | From | Geert Uytterhoeven <> | Subject | Re: [PATCH/RFC] ps3/block: Add ps3vram-ng driver for accessing video RAM as block device |
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On Mon, 9 Mar 2009, Jens Axboe wrote: > On Mon, Mar 09 2009, Jens Axboe wrote: > > On Mon, Mar 09 2009, Geert Uytterhoeven wrote: > > > On Fri, 6 Mar 2009, Jens Axboe wrote: > > > > On Fri, Mar 06 2009, Geert Uytterhoeven wrote: > > > > > On Fri, 6 Mar 2009, Jens Axboe wrote: > > > > > > On Fri, Mar 06 2009, Geert Uytterhoeven wrote: > > > > > > > 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... > > > > > > > > > > > > Certainly. Even just replacing your current mutex with a spinlock during > > > > > > the memcpy() would surely be a lot faster. Or even just grabbing the > > > > > > mutex before calling into the write for the duration of the bio. The way > > > > > > you do it is certain context switch death :-) > > > > > > > > > > It's not just the memcpy(). ps3vram_{up,down}load() call msleep(), so > > > > > I cannot use a spinlock. > > > > > > > > Ah right, I hadn't looked close enough. But putting the mutex_lock() > > > > outside of the bio_for_each_segment() is going to be much faster than > > > > getting/releasing it for each segment. > > > > > > It doesn't seem to make any measurable difference, so I'm gonna leave it for > > > now. > > > > It will depend on where the bio's are coming from. If they are all > > single segment, then there will be no difference. If they contain > > multiple segments, you reduce the lock/release by that amount. > > > > But yeah, just leave it as-is for now. You can send a final patch for > > inclusion though. Unless I'm mistaken, I only saw the original and then > > an incremental patch for changing it to ->make_request_fn? > > There was a full version, my mistake. I got confused by the removal of
Indeed.
> the old driver in another directory :-)
Can you please ack it? Thx!
With kind regards,
Geert Uytterhoeven Software Architect
Sony Techsoft Centre Europe The Corporate Village · Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium
Phone: +32 (0)2 700 8453 Fax: +32 (0)2 700 8622 E-mail: Geert.Uytterhoeven@sonycom.com Internet: http://www.sony-europe.com/
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