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[174.93.89.196]) by smtp.gmail.com with ESMTPSA id x72sm611434qkb.90.2020.11.19.12.02.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Nov 2020 12:02:52 -0800 (PST) Date: Thu, 19 Nov 2020 15:02:50 -0500 From: Peter Xu To: Andrey Gruzdev Subject: Re: [PATCH v3 7/7] introduce simple linear scan rate limiting mechanism Message-ID: <20201119200250.GH6538@xz-x1> References: <20201119125940.20017-1-andrey.gruzdev@virtuozzo.com> <20201119125940.20017-8-andrey.gruzdev@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <20201119125940.20017-8-andrey.gruzdev@virtuozzo.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=peterx@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, RCVD_IN_MSPIKE_H3=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: Juan Quintela , Markus Armbruster , qemu-devel@nongnu.org, "Dr . David Alan Gilbert" , Paolo Bonzini , Den Lunev Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Nov 19, 2020 at 03:59:40PM +0300, Andrey Gruzdev wrote: > Since reading UFFD events and saving paged data are performed > from the same thread, write fault latencies are sensitive to > migration stream stalls. Limiting total page saving rate is a > method to reduce amount of noticiable fault resolution latencies. > > Migration bandwidth limiting is achieved via noticing cases of > out-of-threshold write fault latencies and temporarily disabling > (strictly speaking, severely throttling) saving non-faulting pages. Just curious: have you measured aver/max latency of wr-protected page requests, or better, even its distribution? I believe it should also be relevant to where the snapshot is stored, say, the backend disk of your tests. Is that a file on some fs? I would expect the latency should be still good if e.g. the throughput of the backend file system is decent even without a patch like this, but I might have missed something.. In all cases, it would be very nice if this patch can have the histogram or aver or max latency measured and compared before/after this patch applied. Thanks, -- Peter Xu