From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 82C84C433EF for ; Tue, 14 Jun 2022 13:25:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245363AbiFNNZm (ORCPT ); Tue, 14 Jun 2022 09:25:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42936 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243101AbiFNNZl (ORCPT ); Tue, 14 Jun 2022 09:25:41 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A98B13CFE2 for ; Tue, 14 Jun 2022 06:25:40 -0700 (PDT) Date: Tue, 14 Jun 2022 15:25:37 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1655213138; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=HgXa9L+iV+7zBfhKa3Rr0XV93bVTAQjox2YJMz4AHCM=; b=Aqgy5qT7mH48G22oPeVFUFgifa/KQqsaUyJQtY9dpXLWEPFTOvW4WqCjf3DvJcs8Gy27q2 MEw27SJcu7teRJpWbVvSKDJU7s6Ft94EnzU1BPdJ5b0CvVE7WF9L+LJcaurg3TZOm+hRvC GNKUYFHgApG36uqPj/xkJANXu0b4bQWYMZfgMaMRZXz9l/rC9nFzTKv8Vw2c638s65E2WB 8IlQBIil0o5Kl13wODCSU209ePbs7jrmGUqtt9BYn5vHMHIqDKJB7udj4S7RKvLs7/r1Od kL+T17cI6y1H9IOUkuuzDKMo0kbIIvL5BEHNhJkm9uF0Odf3D1guIOhyH60nBA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1655213138; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=HgXa9L+iV+7zBfhKa3Rr0XV93bVTAQjox2YJMz4AHCM=; b=EBE7d9+UYA5E++I4PSONdHMe8+Fit1/L+J9Q/EsQAzlhNCZCT47ZWw1HksPr1cDxxU/Qua YSVyfNd8EOeK/ACw== From: 'Sebastian Andrzej Siewior' To: David Laight Cc: Davidlohr Bueso , Tyrel Datwyler , "ejb@linux.ibm.com" , "linux-scsi@vger.kernel.org" , "martin.petersen@oracle.com" , "tglx@linutronix.de" , "linuxppc-dev@lists.ozlabs.org" Subject: Re: [PATCH 09/10] scsi/ibmvscsi: Replace srp tasklet with work Message-ID: References: <20220530231512.9729-1-dave@stgolabs.net> <20220530231512.9729-10-dave@stgolabs.net> <7faa88aaf7554545a60561d73597dc4f@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <7faa88aaf7554545a60561d73597dc4f@AcuMS.aculab.com> Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 2022-06-09 15:46:04 [+0000], David Laight wrote: > From: Sebastian Andrzej Siewior > > Sent: 09 June 2022 16:03 > > > > On 2022-05-30 16:15:11 [-0700], Davidlohr Bueso wrote: > > > Tasklets have long been deprecated as being too heavy on the system > > > by running in irq context - and this is not a performance critical > > > path. If a higher priority process wants to run, it must wait for > > > the tasklet to finish before doing so. > > > > > > Process srps asynchronously in process context in a dedicated > > > single threaded workqueue. > > > > I would suggest threaded interrupts instead. The pattern here is the > > same as in the previous driver except here is less locking. > > How long do these actions runs for, and what is waiting for > them to finish? That is something that one with hardware and workload can answer. > These changes seem to drop the priority from above that of the > highest priority RT process down to that of a default priority > user process. > There is no real guarantee that the latter will run 'any time soon'. Not sure I can follow. Using threaded interrupts will run at FIFO-50 by default. Workqueue however is SCHED_OTHER. But then it is not bound to any CPU so it will run on an available CPU. > Consider some workloads I'm setting up where most of the cpu are > likely to spend 90%+ of the time running processes under the RT > scheduler that are processing audio. > > It is quite likely that a non-RT thread (especially one bound > to a specific cpu) won't run for several milliseconds. > (We have to go through 'hoops' to avoid dropping ethernet frames.) > > I'd have thought that some of these kernel threads really > need to run at a 'middling' RT priority. The threaded interrupts do this by default. If you run your own RT threads you need to decide if they are more or less important than the interrupts. > David Sebastian From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7536BC433EF for ; Tue, 14 Jun 2022 13:26:32 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4LMq2t5Xcrz3bt2 for ; Tue, 14 Jun 2022 23:26:30 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; secure) header.d=linutronix.de header.i=@linutronix.de header.a=rsa-sha256 header.s=2020 header.b=Aqgy5qT7; dkim=fail reason="signature verification failed" header.d=linutronix.de header.i=@linutronix.de header.a=ed25519-sha256 header.s=2020e header.b=EBE7d9+U; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linutronix.de (client-ip=193.142.43.55; helo=galois.linutronix.de; envelope-from=bigeasy@linutronix.de; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; secure) header.d=linutronix.de header.i=@linutronix.de header.a=rsa-sha256 header.s=2020 header.b=Aqgy5qT7; dkim=pass header.d=linutronix.de header.i=@linutronix.de header.a=ed25519-sha256 header.s=2020e header.b=EBE7d9+U; dkim-atps=neutral Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4LMq2C3QDCz3bl4 for ; Tue, 14 Jun 2022 23:25:55 +1000 (AEST) Date: Tue, 14 Jun 2022 15:25:37 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1655213138; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=HgXa9L+iV+7zBfhKa3Rr0XV93bVTAQjox2YJMz4AHCM=; b=Aqgy5qT7mH48G22oPeVFUFgifa/KQqsaUyJQtY9dpXLWEPFTOvW4WqCjf3DvJcs8Gy27q2 MEw27SJcu7teRJpWbVvSKDJU7s6Ft94EnzU1BPdJ5b0CvVE7WF9L+LJcaurg3TZOm+hRvC GNKUYFHgApG36uqPj/xkJANXu0b4bQWYMZfgMaMRZXz9l/rC9nFzTKv8Vw2c638s65E2WB 8IlQBIil0o5Kl13wODCSU209ePbs7jrmGUqtt9BYn5vHMHIqDKJB7udj4S7RKvLs7/r1Od kL+T17cI6y1H9IOUkuuzDKMo0kbIIvL5BEHNhJkm9uF0Odf3D1guIOhyH60nBA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1655213138; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=HgXa9L+iV+7zBfhKa3Rr0XV93bVTAQjox2YJMz4AHCM=; b=EBE7d9+UYA5E++I4PSONdHMe8+Fit1/L+J9Q/EsQAzlhNCZCT47ZWw1HksPr1cDxxU/Qua YSVyfNd8EOeK/ACw== From: 'Sebastian Andrzej Siewior' To: David Laight Subject: Re: [PATCH 09/10] scsi/ibmvscsi: Replace srp tasklet with work Message-ID: References: <20220530231512.9729-1-dave@stgolabs.net> <20220530231512.9729-10-dave@stgolabs.net> <7faa88aaf7554545a60561d73597dc4f@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <7faa88aaf7554545a60561d73597dc4f@AcuMS.aculab.com> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Tyrel Datwyler , Davidlohr Bueso , "linux-scsi@vger.kernel.org" , "martin.petersen@oracle.com" , "ejb@linux.ibm.com" , "tglx@linutronix.de" , "linuxppc-dev@lists.ozlabs.org" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 2022-06-09 15:46:04 [+0000], David Laight wrote: > From: Sebastian Andrzej Siewior > > Sent: 09 June 2022 16:03 > > > > On 2022-05-30 16:15:11 [-0700], Davidlohr Bueso wrote: > > > Tasklets have long been deprecated as being too heavy on the system > > > by running in irq context - and this is not a performance critical > > > path. If a higher priority process wants to run, it must wait for > > > the tasklet to finish before doing so. > > > > > > Process srps asynchronously in process context in a dedicated > > > single threaded workqueue. > > > > I would suggest threaded interrupts instead. The pattern here is the > > same as in the previous driver except here is less locking. > > How long do these actions runs for, and what is waiting for > them to finish? That is something that one with hardware and workload can answer. > These changes seem to drop the priority from above that of the > highest priority RT process down to that of a default priority > user process. > There is no real guarantee that the latter will run 'any time soon'. Not sure I can follow. Using threaded interrupts will run at FIFO-50 by default. Workqueue however is SCHED_OTHER. But then it is not bound to any CPU so it will run on an available CPU. > Consider some workloads I'm setting up where most of the cpu are > likely to spend 90%+ of the time running processes under the RT > scheduler that are processing audio. > > It is quite likely that a non-RT thread (especially one bound > to a specific cpu) won't run for several milliseconds. > (We have to go through 'hoops' to avoid dropping ethernet frames.) > > I'd have thought that some of these kernel threads really > need to run at a 'middling' RT priority. The threaded interrupts do this by default. If you run your own RT threads you need to decide if they are more or less important than the interrupts. > David Sebastian