From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kent Overstreet Subject: Re: [PATCH v10 4/8] block: Add bio_reset() Date: Fri, 7 Sep 2012 13:58:23 -0700 Message-ID: <20120907205823.GD16360@google.com> References: <1346970902-10931-1-git-send-email-koverstreet@google.com> <1346970902-10931-5-git-send-email-koverstreet@google.com> <50494F1A.4080207@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <50494F1A.4080207@kernel.dk> Sender: linux-kernel-owner@vger.kernel.org To: Jens Axboe Cc: linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com List-Id: linux-bcache@vger.kernel.org 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... > 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). > 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. > > BTW, I looked over the rest of the patches, and it looks OK to me. Resent them. Thanks!