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bh=VOpNvAmGmsNtzoMJ+JuvpmPoWFaYH49v42cE5SGuJZ0=; b=DRuuYkftuVcEkCTpAkZ62PS1ikuHm5Wqss4cuPTrogRUOPmKKcLb6z9mslackuFkD37joC tDiaKA4C3nY6AjwKV/guGuc9ppZjBvxEV4cfAY5TjJvwaOjdRuOiqimQ3B+cH4s+4Z9rYY lEB7F2N6vMd0YdAWhoWhUGqu+Zh+tiQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-345-zxk9PuFYNBWQiqxFy3bi-g-1; Tue, 22 Sep 2020 13:46:29 -0400 X-MC-Unique: zxk9PuFYNBWQiqxFy3bi-g-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A5F8B109107A; Tue, 22 Sep 2020 17:46:28 +0000 (UTC) Received: from redhat.com (ovpn-114-64.ams2.redhat.com [10.36.114.64]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 074DB5C1D0; Tue, 22 Sep 2020 17:46:20 +0000 (UTC) Date: Tue, 22 Sep 2020 18:46:18 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Vivek Goyal Subject: Re: [PATCH] virtiofsd: Used glib "shared" thread pool Message-ID: <20200922174618.GV1989025@redhat.com> References: <20200921213216.GE13362@redhat.com> <20200922125957.GN1989025@redhat.com> <20200922174255.GC57620@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200922174255.GC57620@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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=216.205.24.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/22 00:31:51 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.455, 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_H5=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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: virtio-fs-list , Miklos Szeredi , qemu-devel@nongnu.org, Stefan Hajnoczi , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Sep 22, 2020 at 01:42:55PM -0400, Vivek Goyal wrote: > On Tue, Sep 22, 2020 at 01:59:57PM +0100, Daniel P. Berrangé wrote: > > On Mon, Sep 21, 2020 at 05:32:16PM -0400, Vivek Goyal wrote: > > > glib offers thread pools and it seems to support "exclusive" and "shared" > > > thread pools. > > > > > > https://developer.gnome.org/glib/stable/glib-Thread-Pools.html#g-thread-pool-new > > > > > > Currently we use "exlusive" thread pools but its performance seems to be > > > poor. I tried using "shared" thread pools and performance seems much > > > better. I posted performance results here. > > > > > > https://www.redhat.com/archives/virtio-fs/2020-September/msg00080.html > > > > > > So lets switch to shared thread pools. We can think of making it optional > > > once somebody can show in what cases exclusive thread pools offer better > > > results. For now, my simple performance tests across the board see > > > better results with shared thread pools. > > > > I'm really curious why there's any perf difference between shared and > > exclusive thread pools in the GLib impl. > > > > Looking at the code the main difference between the two is appears to > > be around the way threads are spawned, specifically around the scheduler > > attributes assigned. > > > > In the shared case, the threads in the pool will have their scheduler > > attributes copied from the very first thread that calls g_thread_pool_new. > > > > In the exclusive case, the threads in the pool will inherit their > > scheduler attributes from the thread which pushs the job that > > causes the worker thread to be created. > > > > By schedular attributes, I mean all the items in the 'struct schedattr' > > filled by sched_getattr() > > > > IOW, if threads in virtiofsd have varying schedular attributes this > > could possibly explain the difference in performance you see between > > the two setups. > > Hi Daniel, > > Few things. > > - I think scheduler attributes are same for the thread creating > pool as well as for thread pushing the job for virtiofsd. > > - My glib2 is old (2.58.3) and I think that did not have sched_getattr() > stuff. > > - One difference I noticed is that in case of shared pool, it does not > create extra threads if client is doing one request at a time. While > exclusive pool seemed to push every request to a new thread in pool > in sort of round robin fashion. It feels keeping requests being served > from same thread helps in this particilar workload case. Yeah, that does sound like a candidate for the cause. I wonder if that was intentional in the GLib design or just an accidental impl they didn't realize had performance implications. Might be worth filing a bug against GLib if someone has free time & motivation to figure out a standalone reproducer to demonstrate the performance difference in the GLib APIs. 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 :| From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 22 Sep 2020 18:46:18 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Message-ID: <20200922174618.GV1989025@redhat.com> References: <20200921213216.GE13362@redhat.com> <20200922125957.GN1989025@redhat.com> <20200922174255.GC57620@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200922174255.GC57620@redhat.com> Subject: Re: [Virtio-fs] [PATCH] virtiofsd: Used glib "shared" thread pool Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= List-Id: Development discussions about virtio-fs List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Vivek Goyal Cc: virtio-fs-list , Miklos Szeredi , qemu-devel@nongnu.org On Tue, Sep 22, 2020 at 01:42:55PM -0400, Vivek Goyal wrote: > On Tue, Sep 22, 2020 at 01:59:57PM +0100, Daniel P. Berrangé wrote: > > On Mon, Sep 21, 2020 at 05:32:16PM -0400, Vivek Goyal wrote: > > > glib offers thread pools and it seems to support "exclusive" and "shared" > > > thread pools. > > > > > > https://developer.gnome.org/glib/stable/glib-Thread-Pools.html#g-thread-pool-new > > > > > > Currently we use "exlusive" thread pools but its performance seems to be > > > poor. I tried using "shared" thread pools and performance seems much > > > better. I posted performance results here. > > > > > > https://www.redhat.com/archives/virtio-fs/2020-September/msg00080.html > > > > > > So lets switch to shared thread pools. We can think of making it optional > > > once somebody can show in what cases exclusive thread pools offer better > > > results. For now, my simple performance tests across the board see > > > better results with shared thread pools. > > > > I'm really curious why there's any perf difference between shared and > > exclusive thread pools in the GLib impl. > > > > Looking at the code the main difference between the two is appears to > > be around the way threads are spawned, specifically around the scheduler > > attributes assigned. > > > > In the shared case, the threads in the pool will have their scheduler > > attributes copied from the very first thread that calls g_thread_pool_new. > > > > In the exclusive case, the threads in the pool will inherit their > > scheduler attributes from the thread which pushs the job that > > causes the worker thread to be created. > > > > By schedular attributes, I mean all the items in the 'struct schedattr' > > filled by sched_getattr() > > > > IOW, if threads in virtiofsd have varying schedular attributes this > > could possibly explain the difference in performance you see between > > the two setups. > > Hi Daniel, > > Few things. > > - I think scheduler attributes are same for the thread creating > pool as well as for thread pushing the job for virtiofsd. > > - My glib2 is old (2.58.3) and I think that did not have sched_getattr() > stuff. > > - One difference I noticed is that in case of shared pool, it does not > create extra threads if client is doing one request at a time. While > exclusive pool seemed to push every request to a new thread in pool > in sort of round robin fashion. It feels keeping requests being served > from same thread helps in this particilar workload case. Yeah, that does sound like a candidate for the cause. I wonder if that was intentional in the GLib design or just an accidental impl they didn't realize had performance implications. Might be worth filing a bug against GLib if someone has free time & motivation to figure out a standalone reproducer to demonstrate the performance difference in the GLib APIs. 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 :|