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([2a00:23c6:9e09:2900:4423:7d1b:b637:c183]) by smtp.gmail.com with ESMTPSA id e29sm1298419wra.7.2020.05.21.13.11.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 21 May 2020 13:11:36 -0700 (PDT) Subject: Re: [PATCH] smp: generic ipi_raise tracepoint To: Nadav Amit Cc: LKML , Thomas Gleixner , Greg Kroah-Hartman , Peter Zijlstra References: <02b57f31-fc0c-df35-57bf-e0a297a7e6c4@gmail.com> <40AA62E7-3AFB-44DC-B4A6-F89E5C914620@vmware.com> From: Wojciech Kudla Message-ID: <767faf00-0dc0-698a-910f-100608d10d81@gmail.com> Date: Thu, 21 May 2020 21:11:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <40AA62E7-3AFB-44DC-B4A6-F89E5C914620@vmware.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/05/2020 20:00, Nadav Amit wrote: >> - if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu))) >> + if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu))) { >> + if (trace_ipi_raise_enabled()) > > Why do you need this check? trace_ipi_raise() will do the same check before > actual tracing: > > if (static_key_false(&__tracepoint_##name.key) > Yes, my motivation for conditional logic was performance-driven. Thanks for pointing out the implicit check. > > In general, I think there are too many trace-points. They look benign(i.e., > free), but can cause worse code to be generated as they behave as a memory > clobber. Many times the same result can be achieved with a probe. > Thank you for the review, I agree this may not be optimal. Let's just stop here. There's a different patch I submitted today that follows Peter's suggestions about smp function calls being much more sensible target for new tracepoints. http://lkml.kernel.org/r/e6141d56-1da1-6c00-198f-cbe4385327ff@gmail.com Thanks, W.