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Wed, 04 Sep 2024 07:49:31 -0700 (PDT) Received: from [192.168.1.116] ([96.43.243.2]) by smtp.gmail.com with ESMTPSA id 8926c6da1cb9f-4ced2de7b11sm3084201173.70.2024.09.04.07.49.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Sep 2024 07:49:30 -0700 (PDT) Message-ID: <4f804d53-6f6c-402c-b8db-db6ab8161f11@kernel.dk> Date: Wed, 4 Sep 2024 08:49:30 -0600 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHSET v6 0/4] Split iowait into two states From: Jens Axboe To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, rafael@kernel.org, daniel.lezcano@linaro.org, linux-pm@vger.kernel.org References: <20240819154259.215504-1-axboe@kernel.dk> <20240904142841.GL4723@noisy.programming.kicks-ass.net> <30eeae06-0d8a-4968-ba57-d723162a0782@kernel.dk> Content-Language: en-US In-Reply-To: <30eeae06-0d8a-4968-ba57-d723162a0782@kernel.dk> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/4/24 8:41 AM, Jens Axboe wrote: > On 9/4/24 8:28 AM, Peter Zijlstra wrote: >> On Mon, Aug 19, 2024 at 09:39:45AM -0600, Jens Axboe wrote: >>> Hi, >>> >>> This is v6 of the patchset where the current in_iowait state is split >>> into two parts: >>> >>> 1) The "task is sleeping waiting on IO", and would like cpufreq goodness >>> in terms of sleep and wakeup latencies. >>> 2) The above, and also accounted as such in the iowait stats. >>> >>> The current ->in_iowait covers both, this series splits it into two types >>> of state so that each can be controlled seperately. >> >> Yeah, but *WHY* !?!? I have some vague memories from last time around, >> but patches should really keep this information. > > To decouple the frequency boost on short waits from the accounting side, > as lots of tooling equates iowait time with busy time and reports it as > such. Yeah that's garbage and a reporting issue, but decades of > education hasn't really improved on that. We should've dumped iowait > once we moved away from 1-2 processor system or had preemptible kernels, > but alas we did not and here we are in 2024. Forgot to mention, it's not *just* an educational thing - lots services of services do mixed network and disk IO, obviously, and they do have some interest in retaining iowait metrics on the disk side. -- Jens Axboe