From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Fri, 7 Jul 2017 13:46:49 +0100 Subject: [PATCH 0/8] io-pgtable lock removal In-Reply-To: <94ba5d4a-0dae-9394-79ef-90da86e49c86@broadcom.com> References: <20170628114609.GD11053@arm.com> <87d53115-3d80-5a3d-6632-c31986cb7018@broadcom.com> <20170704173155.GN22175@arm.com> <6814b246-22f0-bfaa-5002-a269b2735116@broadcom.com> <2d5f5ef3-32b1-76c6-6869-ff980557f8e8@broadcom.com> <20170705084143.GA9378@arm.com> <5149280b-a214-249c-c5e2-3712b1f941d2@broadcom.com> <20170706150838.GB15574@arm.com> <94ba5d4a-0dae-9394-79ef-90da86e49c86@broadcom.com> Message-ID: <20170707124648.GH6735@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Jul 06, 2017 at 11:14:00AM -0700, Ray Jui wrote: > On 7/6/17 8:08 AM, Will Deacon wrote: > > On Wed, Jul 05, 2017 at 04:24:22PM -0700, Ray Jui wrote: > >> However, with the fix patch, I can still see the deadlock message when I > >> have > 32 iperf TX threads active in the system: > > > > Damn. We've been going over this today and the only plausible theory seems > > to be that concurrent TLB syncs are causing the completion to be pushed out, > > resulting in timeouts. > > > > Can you try this patch below, instead of the one I sent before, please? > > > > Thanks, > > > > Will > > > > --->8 > > Good news! I can confirm that with the new patch below, the error log of > "TLB sync timed out" is now gone. I ran 20 iterations of the iperf > client test with 64 threads spread across 8 CPUs. The error message used > to coming out very quickly with just one iteration. But now it's > completely gone. Good, I'll queue this is as a fix then. Thanks for testing! > At the same time, I do seem to observe a slight impact on performance > when multiple threads are used, but I guess that is expected, given that > a spin lock is added to protect the TLB sync. Hopefully that performance will pick up again once we defer the sync to the end of iommu_unmap. Will