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Re: xentrace buffer size, maxcpus and online cpus
- To: Olaf Hering <olaf@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 30 May 2023 10:41:07 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 30 May 2023 08:41:29 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 30.05.2023 09:58, Olaf Hering wrote:
> While looking again through calculate_tbuf_size after a very long time,
> I was wondering why the code uses nr_cpu_ids instead of num_online_cpus.
> In case Xen was booted with maxcpus=N, would it be safe to use N as
> upper limit? I think this would increase the per-cpu buffer size for
> each active pcpu, and as a result more events could be captured.
Using this N would be correct afaict, but that N isn't num_online_cpus().
CPUs may have been offlined by the time trace buffers are initialized, so
without looking too closely I think it would be num_present_cpus() that
you're after.
Jan
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