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(p200300cbc7072c00d4ac0d2c4aeedac1.dip0.t-ipconnect.de. [2003:cb:c707:2c00:d4ac:d2c:4aee:dac1]) by smtp.gmail.com with ESMTPSA id bv16-20020a0560001f1000b0022e6f0d0d7csm16223245wrb.18.2022.10.19.05.36.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Oct 2022 05:36:34 -0700 (PDT) Message-ID: <85d09f43-127b-0111-177e-38baf8c54c73@redhat.com> Date: Wed, 19 Oct 2022 14:36:33 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.1 Subject: Re: [PATCH v3 0/7] hostmem: NUMA-aware memory preallocation using ThreadContext Content-Language: en-US To: qemu-devel@nongnu.org Cc: Michal Privoznik , Igor Mammedov , "Michael S. Tsirkin" , Paolo Bonzini , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , Eduardo Habkost , "Dr . David Alan Gilbert" , Eric Blake , Markus Armbruster , Richard Henderson , Stefan Weil References: <20221014134720.168738-1-david@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20221014134720.168738-1-david@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.256, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 14.10.22 15:47, David Hildenbrand wrote: > This is a follow-up on "util: NUMA aware memory preallocation" [1] by > Michal. > > Setting the CPU affinity of threads from inside QEMU usually isn't > easily possible, because we don't want QEMU -- once started and running > guest code -- to be able to mess up the system. QEMU disallows relevant > syscalls using seccomp, such that any such invocation will fail. > > Especially for memory preallocation in memory backends, the CPU affinity > can significantly increase guest startup time, for example, when running > large VMs backed by huge/gigantic pages, because of NUMA effects. For > NUMA-aware preallocation, we have to set the CPU affinity, however: > > (1) Once preallocation threads are created during preallocation, management > tools cannot intercept anymore to change the affinity. These threads > are created automatically on demand. > (2) QEMU cannot easily set the CPU affinity itself. > (3) The CPU affinity derived from the NUMA bindings of the memory backend > might not necessarily be exactly the CPUs we actually want to use > (e.g., CPU-less NUMA nodes, CPUs that are pinned/used for other VMs). > > There is an easy "workaround". If we have a thread with the right CPU > affinity, we can simply create new threads on demand via that prepared > context. So, all we have to do is setup and create such a context ahead > of time, to then configure preallocation to create new threads via that > environment. > > So, let's introduce a user-creatable "thread-context" object that > essentially consists of a context thread used to create new threads. > QEMU can either try setting the CPU affinity itself ("cpu-affinity", > "node-affinity" property), or upper layers can extract the thread id > ("thread-id" property) to configure it externally. > > Make memory-backends consume a thread-context object > (via the "prealloc-context" property) and use it when preallocating to > create new threads with the desired CPU affinity. Further, to make it > easier to use, allow creation of "thread-context" objects, including > setting the CPU affinity directly from QEMU, before enabling the > sandbox option. > > > Quick test on a system with 2 NUMA nodes: > > Without CPU affinity: > time qemu-system-x86_64 \ > -object memory-backend-memfd,id=md1,hugetlb=on,hugetlbsize=2M,size=64G,prealloc-threads=12,prealloc=on,host-nodes=0,policy=bind \ > -nographic -monitor stdio > > real 0m5.383s > real 0m3.499s > real 0m5.129s > real 0m4.232s > real 0m5.220s > real 0m4.288s > real 0m3.582s > real 0m4.305s > real 0m5.421s > real 0m4.502s > > -> It heavily depends on the scheduler CPU selection > > With CPU affinity: > time qemu-system-x86_64 \ > -object thread-context,id=tc1,node-affinity=0 \ > -object memory-backend-memfd,id=md1,hugetlb=on,hugetlbsize=2M,size=64G,prealloc-threads=12,prealloc=on,host-nodes=0,policy=bind,prealloc-context=tc1 \ > -sandbox enable=on,resourcecontrol=deny \ > -nographic -monitor stdio > > real 0m1.959s > real 0m1.942s > real 0m1.943s > real 0m1.941s > real 0m1.948s > real 0m1.964s > real 0m1.949s > real 0m1.948s > real 0m1.941s > real 0m1.937s > > On reasonably large VMs, the speedup can be quite significant. > > While this concept is currently only used for short-lived preallocation > threads, nothing major speaks against reusing the concept for other > threads that are harder to identify/configure -- except that > we need additional (idle) context threads that are otherwise left unused. > > This series does not yet tackle concurrent preallocation of memory > backends. Memory backend objects are created and memory is preallocated one > memory backend at a time -- and there is currently no way to do > preallocation asynchronously. > > [1] https://lkml.kernel.org/r/ffdcd118d59b379ede2b64745144165a40f6a813.1652165704.git.mprivozn@redhat.com > I'm happy for more feedback and will wait some more. But if there is none, I'll most probably merge this myself by the end of next week. Cheers! -- Thanks, David / dhildenb