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McKenney" Cc: linux-kernel@vger.kernel.org, John Stultz , Thomas Gleixner , Stephen Boyd , Feng Tang Subject: Re: [PATCH] clocksource: Skip watchdog check for large watchdog intervals Message-ID: <20240104163050.GC3303@incl> References: <20240103112113.GA6108@incl> <5b8fd9ba-1622-4ec7-b3cc-2db3a78122f1@paulmck-laptop> 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-Disposition: inline In-Reply-To: <5b8fd9ba-1622-4ec7-b3cc-2db3a78122f1@paulmck-laptop> User-Agent: Mutt/1.10.1 (2018-07-13) X-Spam-Level: X-Spam-Level: Authentication-Results: smtp-out1.suse.de; dkim=pass header.d=suse.de header.s=susede2_rsa header.b="IguwM/Rt"; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=Iqzz7IPx X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-3.43 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; URIBL_BLOCKED(0.00)[suse.de:dkim]; DWL_DNSWL_MED(-2.00)[suse.de:dkim]; RCPT_COUNT_FIVE(0.00)[6]; NEURAL_HAM_SHORT(-0.20)[-1.000]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+]; MX_GOOD(-0.01)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_NOT_FQDN(0.50)[]; RCVD_TLS_ALL(0.00)[]; BAYES_HAM(-0.42)[78.11%] X-Spam-Score: -3.43 X-Rspamd-Queue-Id: 30720220D1 X-Spam-Flag: NO On Wed, Jan 03, 2024 at 02:08:08PM -0800, Paul E. McKenney wrote: > I believe that there were concerns about a similar approach in the case > where the jiffies counter is the clocksource I ran a few simple tests on a 2 NUMA node Intel machine and found nothing so far. I tried booting with clocksource=jiffies and I changed the "nr_online_nodes <= 4" check in tsc_clocksource_as_watchdog() to enable the watchdog on my machine. I have a debugging module that monitors clocksource and watchdog reads in clocksource_watchdog() with kprobes. I see the cs/wd reads executed roughly every 0.5 second, as expected. When the machine is idle the average watchdog interval is 501.61 milliseconds (+-15.57 ms, with a minimum of 477.07 ms and a maximum of 517.93 ms). The result is similar when the CPUs of the machine are fully saturated with netperf processes. I also tried booting with clocksource=jiffies and tsc=watchdog. The watchdog interval was similar to the previous test. AFAIK, the jiffies clocksource does get checked by the watchdog itself. And with that, I have run out of ideas. -- Jiri Wiesner SUSE Labs