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Thu, 23 Jul 2020 09:00:30 +0000 (UTC) Date: Thu, 23 Jul 2020 10:00:27 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Richard Henderson Subject: Re: [PATCH v2 06/12] accel/tcg: better handle memory constrained systems Message-ID: <20200723090027.GB2615312@redhat.com> References: <20200722062902.24509-1-alex.bennee@linaro.org> <20200722062902.24509-7-alex.bennee@linaro.org> <5d26e26f-55f7-5b74-bb9e-b97ea1040c05@linaro.org> <87ft9jtsw5.fsf@linaro.org> <20200722163722.GS2324845@redhat.com> <0efbcac2-d2f4-de96-63a1-ba7cd485a1e6@linaro.org> MIME-Version: 1.0 In-Reply-To: <0efbcac2-d2f4-de96-63a1-ba7cd485a1e6@linaro.org> User-Agent: Mutt/1.14.5 (2020-06-23) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/22 22:13:02 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, URIBL_BLOCKED=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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: fam@euphon.net, Alex =?utf-8?Q?Benn=C3=A9e?= , qemu-devel@nongnu.org, Christian Ehrhardt , f4bug@amsat.org, cota@braap.org, Paolo Bonzini , aurelien@aurel32.net, Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 22, 2020 at 12:02:59PM -0700, Richard Henderson wrote: > On 7/22/20 9:44 AM, Daniel P. Berrangé wrote: > > OpenStack uses TCG in alot of their CI infrastructure for example > > and runs multiple VMs. If there's 4 VMs, that's another 4 GB of > > RAM usage just silently added on top of the explicit -m value. > > > > I wouldn't be surprised if this pushes CI into OOM, even without > > containers or cgroups being involved, as they have plenty of other > > services consuming RAM in the CI VMs. > > I would hope that CI would also supply a -tb_size to go along with that -m > value. Because we really can't guess on their behalf. I've never even seen mention of -tb_size argument before myself, nor seen anyone else using it and libvirt doesn't set it, so I think this is not a valid assumption. > > The commit 600e17b261555c56a048781b8dd5ba3985650013 talks about this > > minimizing codegen cache flushes, but doesn't mention the real world > > performance impact of eliminating those flushes ? > > Somewhere on the mailing list was this info. It was so dreadfully slow it was > *really* noticable. Timeouts everywhere. > > > Presumably this makes the guest OS boot faster, but what's the before > > and after time ? And what's the time like for values in between the > > original 32mb and the new 1 GB ? > > But it wasn't "the original 32MB". > It was the original "ram_size / 4", until that broke due to argument parsing > ordering. Hmm, 600e17b261555c56a048781b8dd5ba3985650013 says it was 32 MB as the default in its commit message, which seems to match the code doing #define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (32 * MiB) > I don't know what CI usually uses, but I usually use at least -m 4G, sometimes > more. What's the libvirt default? There's no default memory size - its up to whomever/whatever creates the VMs to choose how much RAM is given. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|