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[174.93.75.200]) by smtp.gmail.com with ESMTPSA id z3sm637795qkj.40.2021.06.09.11.57.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Jun 2021 11:57:04 -0700 (PDT) Date: Wed, 9 Jun 2021 14:57:03 -0400 From: Peter Xu To: "Dr. David Alan Gilbert" Subject: Re: [PATCH] hmp: Add "calc_dirty_rate" and "info dirty_rate" cmds Message-ID: References: <20210601005708.189888-1-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: 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: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.199, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=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: Chuan Zheng , Leonardo Bras Soares Passos , huangy81@chinatelecom.cn, qemu-devel@nongnu.org, Juan Quintela Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Jun 08, 2021 at 08:36:23PM +0100, Dr. David Alan Gilbert wrote: > * Peter Xu (peterx@redhat.com) wrote: > > On Tue, Jun 08, 2021 at 07:49:56PM +0100, Dr. David Alan Gilbert wrote: > > > * Peter Xu (peterx@redhat.com) wrote: > > > > These two commands are missing when adding the QMP sister commands. Add them, > > > > so developers can play with them easier. > > > > > > > > Cc: Dr. David Alan Gilbert > > > > Cc: Juan Quintela > > > > Cc: Leonardo Bras Soares Passos > > > > Cc: Chuan Zheng > > > > Cc: huangy81@chinatelecom.cn > > > > Signed-off-by: Peter Xu > > > > > > Reviewed-by: Dr. David Alan Gilbert > > > > > > > --- > > > > PS: I really doubt whether this is working as expected... I ran one 200MB/s > > > > workload inside, what I measured is 20MB/s with current algorithm... Sampling > > > > 512 pages out of 1G mem is not wise enough I guess, especially that assumes > > > > dirty workload is spread across the memories while it's normally not the case.. > > > > > > What size of address space did you dirty - was it 20MB? > > > > IIRC it was either 200M or 500M, based on a 1G small VM. > > What was your sample time ? 10 seconds; I used the same sample time for below runs: https://lore.kernel.org/qemu-devel/YMEFqfYZVhsinNN+@t490s/ A large sample time does make dirty rate less indeed, as the same dirty page could be written again as 1 single page dirtyed in the host (while it's counted twice in the guest dirty workload). This effect should happen too if we further extend calc_dirty_rate with KVM_GET_DIRTY_LOG in the future as the 3rd method besides dirty ring. >From that pov, dirty ring is easier to be more "accurate" (I don't know whether it's suitable to say it's accurate; it's just easier to trap cases like writting to same page multiple times within a period), as the ring size is normally very limited (e.g. 4096 pages per vcpu), so even the guest workload writes the same page twice, as long as there's a ring collect between the two writes, they'll be counted twice too (each collect will reprotect the pages). -- Peter Xu