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(p200300cbc704e6003a4af000b0854839.dip0.t-ipconnect.de. [2003:cb:c704:e600:3a4a:f000:b085:4839]) by smtp.gmail.com with ESMTPSA id w10-20020a05600c474a00b003a5f54e3bbbsm15847406wmo.38.2022.10.10.04.18.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 10 Oct 2022 04:18:57 -0700 (PDT) Message-ID: <23dd0ce0-5393-3aa0-affe-11277c6a123b@redhat.com> Date: Mon, 10 Oct 2022 13:18:56 +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 v2 0/7] hostmem: NUMA-aware memory preallocation using ThreadContext Content-Language: en-US To: "Dr. David Alan Gilbert" Cc: qemu-devel@nongnu.org, Michal Privoznik , Igor Mammedov , "Michael S. Tsirkin" , Paolo Bonzini , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , Eduardo Habkost , Eric Blake , Markus Armbruster , Richard Henderson , Stefan Weil References: <20221010091117.88603-1-david@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-2.007, RCVD_IN_DNSWL_NONE=-0.0001, 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 10.10.22 12:40, Dr. David Alan Gilbert wrote: > * David Hildenbrand (david@redhat.com) 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. Hi Dave, > > Since you seem to have a full set of r-b's - do you intend to merge this > as-is or do the cuncurrenct preallocation first? I intent to merge this as is, as it provides a benefit as it stands and concurrent preallcoation might not require user interface changes. I do have some ideas on how to implement concurrent preallocation, but it needs more thought (and more importantly, time). -- Thanks, David / dhildenb