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([2001:b07:6468:f312:e1d2:138e:4eff:42cb]) by smtp.gmail.com with ESMTPSA id e12sm3503089wro.52.2020.06.18.05.42.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 18 Jun 2020 05:42:20 -0700 (PDT) Subject: Re: [PATCH 0/7] misc: Reduce QEMUTimer pressure by using lower precision when possible To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org References: <20200616075121.12837-1-f4bug@amsat.org> From: Paolo Bonzini Message-ID: <80230616-1927-e861-98f5-b9aaf2fe03b7@redhat.com> Date: Thu, 18 Jun 2020 14:42:18 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=pbonzini@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/18 01:21:16 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: Kevin Wolf , Peter Maydell , qemu-block@nongnu.org, Corey Minyard , David Hildenbrand , Andrew Jeffery , "Michael S. Tsirkin" , Max Reitz , qemu-arm@nongnu.org, Joel Stanley , =?UTF-8?Q?C=c3=a9dric_Le_Goater?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 18/06/20 14:26, Philippe Mathieu-Daudé wrote: >> This is in principle a very good idea; however, util/qemu-timer.c does >> not use the scale to coalesce low-precision timers with nearby >> high-precision ones. > IOW this doesn't reduce the pressure, but simply makes the code easier? Easier, or harder depending on the point of view. The reason why scale exists is just because QEMU_CLOCK_REALTIME used to be millisecond based; having to scale based on the clock was really ugly code, and furthermore the scale provides an easy way to switch timers from one clock to another without having to modify every deadline computation. One might argue that the scale adds to QEMU's cognitive weight for little benefit. You might counter-argue that having to scale up to nanoseconds every time is a pain in the ass, and I am not sure which side I actually agree with. > Only the cover mentions 'pressure', so maybe the patches can still be > reviewed/queued in their current state? Yes, of course. Paolo