From mboxrd@z Thu Jan 1 00:00:00 1970 From: vinod.koul@intel.com (Vinod Koul) Date: Fri, 28 Jul 2017 08:45:01 +0530 Subject: [PATCH 2/6] dma: bcm-sba-raid: Peek mbox when we are left with no free requests In-Reply-To: References: <1501047404-14456-1-git-send-email-anup.patel@broadcom.com> <1501047404-14456-3-git-send-email-anup.patel@broadcom.com> <20170726171028.GJ3053@localhost> Message-ID: <20170728031500.GS3053@localhost> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Jul 27, 2017 at 10:25:25AM +0530, Anup Patel wrote: > On Wed, Jul 26, 2017 at 10:40 PM, Vinod Koul wrote: > > On Wed, Jul 26, 2017 at 11:06:40AM +0530, Anup Patel wrote: > >> We should peek mbox channels when we are left with no free > >> sba_requests in sba_alloc_request() > > > > and why is the world should we do that, how does that help?? > > When setting up RAID array on several NVMe disk we observed > that sba_alloc_request() start failing (due to no free requests left) > and RAID array setup becomes very slow. > > Doing mbox channel peek when we have no free requests left, > improves performance of RAID array setup. How about documenting this tribal knowledge in the changelog. Changelogs are very useful, 6 months down the line, you will struggle to remember why this was changed.. > > This change is inspired from mv_chan_alloc_slot() implemented > in drivers/dma/mv_xor.c > > Regards, > Anup -- ~Vinod