On Tue, May 26 2009, FUJITA Tomonori wrote: > On Mon, 25 May 2009 18:45:25 -0700 > Roland Dreier <rdreier@xxxxxxxxx> wrote: > > > > Ideally there should be a MACRO that is defined to WORD_SIZE on cache-coherent > > > ARCHs and to SMP_CACHE_BYTES on none-cache-coherent systems and use that size > > > at the __align() attribute. (So only stupid ARCHES get hurt) > > > > this seems to come up repeatedly -- I had a proposal a _long_ time ago > > that never quite got merged, cf http://lwn.net/Articles/2265/ and > > http://lwn.net/Articles/2269/ -- from 2002 (!?). The idea is to go a > > Yeah, I think that Benjamin did last time: > > http://www.mail-archive.com/linux-scsi@xxxxxxxxxxxxxxx/msg12632.html > > IIRC, James didn't like it so I wrote the current code. I didn't see > any big performance difference with scsi_debug: > > http://marc.info/?l=linux-scsi&m=120038907123706&w=2 > > Jens, you see the performance difference due to this unification? Yes, it's definitely a worth while optimization. The problem isn't as such this specific allocation, it's the total number of allocations we do for a piece of IO. This sense buffer one is just one of many, I'm continually working to reduce them. If we get rid of this one and add the ->alloc_cmd() stuff, we can kill one more. The bio path already lost one. So in the IO stack, we went from 6 allocations to 3 for a piece of IO. And then it starts to add up. Even at just 30-50k iops, that's more than 1% of time in the testing I did. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
