On 2012-09-07 14:58, Kent Overstreet wrote: > On Thu, Sep 06, 2012 at 07:34:18PM -0600, Jens Axboe wrote: >> On 2012-09-06 16:34, Kent Overstreet wrote: >>> Reusing bios is something that's been highly frowned upon in the past, >>> but driver code keeps doing it anyways. If it's going to happen anyways, >>> we should provide a generic method. >>> >>> This'll help with getting rid of bi_destructor - drivers/block/pktcdvd.c >>> was open coding it, by doing a bio_init() and resetting bi_destructor. >>> >>> This required reordering struct bio, but the block layer is not yet >>> nearly fast enough for any cacheline effects to matter here. >> >> That's an odd and misplaced comment. Was just doing testing today at 5M >> IOPS, and even years back we've had cache effects for O_DIRECT in higher >> speed setups. > > Ah, I wasn't aware that you were pushing that many iops through the > block layer - most I've tested myself was around 1M. It wouldn't > surprise me if cache effects in struct bio mattered around 5M... 5M is nothing, just did 13.5M :-) But we can reshuffle for now. As mentioned, we're way overdue for a decent look at cache profiling in any case. >> That said, we haven't done cache analysis in a long time. So moving >> members around isn't necessarily a huge deal. > > Ok, good to know. I've got another patch coming later that reorders > struct bio a bit more, for immutable bvecs (bi_sector, bi_size, bi_idx > go into a struct bvec_iter together). OK >> Lastly, this isn't a great commit message for other reasons. Anyone can >> see that it moves members around. It'd be a lot better to explain _why_ >> it is reordering the struct. > > Yeah, I suppose so. Will keep that in mind for the next patch. Thanks. >> BTW, I looked over the rest of the patches, and it looks OK to me. > > Resent them. Thanks! Got it. -- Jens Axboe -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
