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[82.30.61.225]) by smtp.gmail.com with ESMTPSA id m4-20020a05600c3b0400b003c6bd12ac27sm1360524wms.37.2022.10.10.03.40.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Oct 2022 03:40:27 -0700 (PDT) Date: Mon, 10 Oct 2022 11:40:25 +0100 From: "Dr. David Alan Gilbert" To: David Hildenbrand Cc: qemu-devel@nongnu.org, Michal Privoznik , Igor Mammedov , "Michael S. Tsirkin" , Paolo Bonzini , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Eduardo Habkost , Eric Blake , Markus Armbruster , Richard Henderson , Stefan Weil Subject: Re: [PATCH v2 0/7] hostmem: NUMA-aware memory preallocation using ThreadContext Message-ID: References: <20221010091117.88603-1-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20221010091117.88603-1-david@redhat.com> User-Agent: Mutt/2.2.7 (2022-08-07) Received-SPF: pass client-ip=170.10.129.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, 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" * 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. 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? Dave > [1] https://lkml.kernel.org/r/ffdcd118d59b379ede2b64745144165a40f6a813.1652165704.git.mprivozn@redhat.com > > v1 -> v2: > * Fixed some minor style nits > * "util: Introduce ThreadContext user-creatable object" > -> Impove documentation and patch description. [Markus] > * "util: Add write-only "node-affinity" property for ThreadContext" > -> Impove documentation and patch description. [Markus] > > RFC -> v1: > * "vl: Allow ThreadContext objects to be created before the sandbox option" > -> Move parsing of the "name" property before object_create_pre_sandbox > * Added RB's > > Cc: Michal Privoznik > Cc: Igor Mammedov > Cc: "Michael S. Tsirkin" > Cc: Paolo Bonzini > Cc: "Daniel P. Berrangé" > Cc: Eduardo Habkost > Cc: Dr. David Alan Gilbert > Cc: Eric Blake > Cc: Markus Armbruster > Cc: Richard Henderson > Cc: Stefan Weil > > David Hildenbrand (7): > util: Cleanup and rename os_mem_prealloc() > util: Introduce qemu_thread_set_affinity() and > qemu_thread_get_affinity() > util: Introduce ThreadContext user-creatable object > util: Add write-only "node-affinity" property for ThreadContext > util: Make qemu_prealloc_mem() optionally consume a ThreadContext > hostmem: Allow for specifying a ThreadContext for preallocation > vl: Allow ThreadContext objects to be created before the sandbox > option > > backends/hostmem.c | 13 +- > hw/virtio/virtio-mem.c | 2 +- > include/qemu/osdep.h | 19 +- > include/qemu/thread-context.h | 57 ++++++ > include/qemu/thread.h | 4 + > include/sysemu/hostmem.h | 2 + > meson.build | 16 ++ > qapi/qom.json | 28 +++ > softmmu/cpus.c | 2 +- > softmmu/vl.c | 36 +++- > util/meson.build | 1 + > util/oslib-posix.c | 39 ++-- > util/oslib-win32.c | 8 +- > util/qemu-thread-posix.c | 70 +++++++ > util/qemu-thread-win32.c | 12 ++ > util/thread-context.c | 362 ++++++++++++++++++++++++++++++++++ > 16 files changed, 641 insertions(+), 30 deletions(-) > create mode 100644 include/qemu/thread-context.h > create mode 100644 util/thread-context.c > > -- > 2.37.3 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK