lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date:   Thu, 21 May 2020 21:11:36 +0100
From:   Wojciech Kudla <>
To:     Nadav Amit <>
Cc:     LKML <>,
        Thomas Gleixner <>,
        Greg Kroah-Hartman <>,
        Peter Zijlstra <>
Subject: Re: [PATCH] smp: generic ipi_raise tracepoint

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.


Powered by blists - more mailing lists