From: Wojciech Kudla <wk.kernel@gmail.com>
To: Nadav Amit <namit@vmware.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] smp: generic ipi_raise tracepoint
Date: Thu, 21 May 2020 21:11:36 +0100 [thread overview]
Message-ID: <767faf00-0dc0-698a-910f-100608d10d81@gmail.com> (raw)
In-Reply-To: <40AA62E7-3AFB-44DC-B4A6-F89E5C914620@vmware.com>
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.
prev parent reply other threads:[~2020-05-21 20:11 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-20 13:17 [PATCH] smp: generic ipi_raise tracepoint Wojciech Kudla
2020-05-20 13:33 ` Peter Zijlstra
2020-05-20 13:42 ` Wojciech Kudla
2020-05-20 13:51 ` Peter Zijlstra
2020-05-21 10:45 ` kbuild test robot
2020-05-21 19:00 ` Nadav Amit
2020-05-21 20:11 ` Wojciech Kudla [this message]
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