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Fri, 25 Sep 2020 09:11:42 -0400 (EDT) Date: Fri, 25 Sep 2020 09:11:42 -0400 From: Vivek Goyal To: "Dr. David Alan Gilbert" Subject: Re: tools/virtiofs: Multi threading seems to hurt performance Message-ID: <20200925131142.GC132653@redhat.com> References: <20200918213436.GA3520@redhat.com> <20200921153243.GK3221@work-vm> <20200922102531.GA2837@work-vm> <20200922174733.GD57620@redhat.com> <20200925121127.GI2873@work-vm> MIME-Version: 1.0 In-Reply-To: <20200925121127.GI2873@work-vm> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vgoyal@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=vgoyal@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/25 01:07:33 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.199, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: jose.carlos.venegas.munoz@intel.com, qemu-devel@nongnu.org, cdupontd@redhat.com, virtio-fs-list , Stefan Hajnoczi , archana.m.shinde@intel.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Sep 25, 2020 at 01:11:27PM +0100, Dr. David Alan Gilbert wrote: > * Vivek Goyal (vgoyal@redhat.com) wrote: > > On Tue, Sep 22, 2020 at 11:25:31AM +0100, Dr. David Alan Gilbert wrote: > > > * Dr. David Alan Gilbert (dgilbert@redhat.com) wrote: > > > > Hi, > > > > I've been doing some of my own perf tests and I think I agree > > > > about the thread pool size; my test is a kernel build > > > > and I've tried a bunch of different options. > > > > > > > > My config: > > > > Host: 16 core AMD EPYC (32 thread), 128G RAM, > > > > 5.9.0-rc4 kernel, rhel 8.2ish userspace. > > > > 5.1.0 qemu/virtiofsd built from git. > > > > Guest: Fedora 32 from cloud image with just enough extra installed for > > > > a kernel build. > > > > > > > > git cloned and checkout v5.8 of Linux into /dev/shm/linux on the host > > > > fresh before each test. Then log into the guest, make defconfig, > > > > time make -j 16 bzImage, make clean; time make -j 16 bzImage > > > > The numbers below are the 'real' time in the guest from the initial make > > > > (the subsequent makes dont vary much) > > > > > > > > Below are the detauls of what each of these means, but here are the > > > > numbers first > > > > > > > > virtiofsdefault 4m0.978s > > > > 9pdefault 9m41.660s > > > > virtiofscache=none 10m29.700s > > > > 9pmmappass 9m30.047s > > > > 9pmbigmsize 12m4.208s > > > > 9pmsecnone 9m21.363s > > > > virtiofscache=noneT1 7m17.494s > > > > virtiofsdefaultT1 3m43.326s > > > > > > > > So the winner there by far is the 'virtiofsdefaultT1' - that's > > > > the default virtiofs settings, but with --thread-pool-size=1 - so > > > > yes it gives a small benefit. > > > > But interestingly the cache=none virtiofs performance is pretty bad, > > > > but thread-pool-size=1 on that makes a BIG improvement. > > > > > > Here are fio runs that Vivek asked me to run in my same environment > > > (there are some 0's in some of the mmap cases, and I've not investigated > > > why yet). > > > > cache=none does not allow mmap in case of virtiofs. That's when you > > are seeing 0. > > > > >virtiofs is looking good here in I think all of the cases; > > > there's some division over which cinfig; cache=none > > > seems faster in some cases which surprises me. > > > > I know cache=none is faster in case of write workloads. It forces > > direct write where we don't call file_remove_privs(). While cache=auto > > goes through file_remove_privs() and that adds a GETXATTR request to > > every WRITE request. > > Can you point me to how cache=auto causes the file_remove_privs? fs/fuse/file.c fuse_cache_write_iter() { err = file_remove_privs(file); } Above path is taken when cache=auto/cache=always is used. If virtiofsd is running with noxattr, then it does not impose any cost. But if xattr are enabled, then every WRITE first results in a getxattr(security.capability) and that slows down WRITES tremendously. When cache=none is used, we go through following path instead. fuse_direct_write_iter() and it does not have file_remove_privs(). We set a flag in WRITE request to tell server to kill suid/sgid/security.capability, instead. fuse_direct_io() { ia->write.in.write_flags |= FUSE_WRITE_KILL_PRIV } Vivek