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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43bbb15841dsm16541775e9.1.2025.03.02.04.05.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 02 Mar 2025 04:05:31 -0800 (PST) Date: Sun, 2 Mar 2025 12:05:30 +0000 From: David Laight To: Attila Fazekas Cc: qyousef@layalina.io, dietmar.eggemann@arm.com, frederic@kernel.org, jstultz@google.com, juri.lelli@redhat.com, linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, rostedt@goodmis.org, saravanak@google.com, tglx@linutronix.de, vincent.guittot@linaro.org Subject: Re: [PATCH] Kconfig.hz: Change default HZ to 1000 Message-ID: <20250302120530.1e742e06@pumpkin> In-Reply-To: <20250228103304.302289-1-afazekas@redhat.com> References: <20250210001915.123424-1-qyousef@layalina.io> <20250228103304.302289-1-afazekas@redhat.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 28 Feb 2025 11:33:04 +0100 Attila Fazekas wrote: > The 250Hz was set as a middle ground. > > There are still workloads which sensitive to cache misses > and to the time spent in ticks. > > You still can loose ~1% performance with higher Hz, > It might not sound much, but if you are running thousands > of servers 1% loss can be a high cost. > > There are many workloads out there where 100Hz is the better choice. Are there are real issues with changing HZ to 1000, but adding an option for the timer tick interval (in ms). So 'jiffies' would always count milliseconds. That would make is easy to make the actual 'clock tick' be boot time selectable (or run-time if you get brave!). The 'timer wheel' code would really need to work on actual ticks, but I doubt nothing else cares. That would allow HZ be the same for all architectures, even though m68k might really want a 50Hz interrupt. That is much better than any plan to make HZ a variable - which will bloat code (and with divisions) and not be valid for static initialisers. David