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[34.86.148.56]) by smtp.gmail.com with ESMTPSA id vv14-20020a05620a562e00b00787acc6a3c7sm126403qkn.65.2024.02.22.10.42.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Feb 2024 10:42:16 -0800 (PST) Date: Thu, 22 Feb 2024 13:42:16 -0500 From: Willem de Bruijn To: Marcelo Tosatti , Willem de Bruijn Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Jakub Kicinski , Eric Dumazet , Frederic Weisbecker , Valentin Schneider Message-ID: <65d795888e904_2c3076294d2@willemb.c.googlers.com.notmuch> In-Reply-To: References: <65d7640c7983b_2bd671294c3@willemb.c.googlers.com.notmuch> Subject: Re: [PATCH] net/core/dev.c: enable timestamp static key if CPU isolation is configured Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Marcelo Tosatti wrote: > On Thu, Feb 22, 2024 at 10:11:08AM -0500, Willem de Bruijn wrote: > > Marcelo Tosatti wrote: > > > For systems that use CPU isolation (via nohz_full), creating or destroying > > > a socket with timestamping (SOF_TIMESTAMPING_OPT_TX_SWHW) might cause a > > > static key to be enabled/disabled. This in turn causes undesired > > > IPIs to isolated CPUs. > > > > This refers to SOF_TIMESTAMPING_RX_SOFTWARE, not SOF_TIMESTAMPING_OPT_TX_SWHW. > > See also sock_set_timestamping. > > Willem, > > This test program does trigger the static key change: > > int main (void) > { > int option = SOF_TIMESTAMPING_OPT_TX_SWHW; > int sock_fd; > int ret; > int pid_fd; > pid_t pid; > char buf[50]; > > ... > > /* set the timestamping option > * this is to trigger the IPIs that notify all cpus of the change > */ > if (setsockopt(sock_fd, SOL_SOCKET, SO_TIMESTAMP, &option, sizeof (option)) < 0) { > printf("Could not enable timestamping option %x", (unsigned int)option); > close(sock_fd); > return 0; > } > ... > That is because you call SO_TIMESTAMP, which interprets option as a boolean. The SOF_ flags apply to setsockopt SO_TIMESTAMPING.