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Re: xentrace buffer size, maxcpus and online cpus
- To: Olaf Hering <olaf@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 16 Jun 2023 13:52:17 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Juergen Gross <jgross@xxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>
- Delivery-date: Fri, 16 Jun 2023 11:52:57 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.06.2023 13:47, Olaf Hering wrote:
> Wed, 31 May 2023 11:05:52 +0200 Jan Beulich <jbeulich@xxxxxxxx>:
>
>> As said before, num_online_cpus() will under-report for the purpose
>> here, as CPUs may have been brought offline, and may be brought online
>> again later (independent of the use of "maxcpus=").
>
> It turned out, commit 74584a367051bc0d6f4b96fd360fa7bc6538fc39 broke
> the expected behavior. But to me it is unclear what bug was fixed by
> this commit.
Hmm, I find title and description quite clear there.
> If I read alloc_trace_bufs correctly, it already operates on online
> cpus. And __trace_var will do nothing if called on a cpu which was
> not online, t_bufs will likely be NULL.
Yielding an incomplete overall trace, at best.
> To me it looks like commit 74584a367051bc0d6f4b96fd360fa7bc6538fc39
> could be reverted.
I don't think so. I'll add George to Cc as well, as he's the maintainer
of this stuff.
Jan
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