On 30/08/18 11:28, Juergen Gross wrote:
> On 30/08/18 10:26, Jan Beulich wrote:
>>>>> On 30.08.18 at 09:52, <jgr...@suse.com> wrote:
>>> @@ -202,7 +202,7 @@ static int alloc_trace_bufs(unsigned int pages)
>>> * Allocate buffers for all of the cpus.
>>> * If any fails, deallocate what you have so far and exit.
>>> */
>>> - for_each_online_cpu(cpu)
>>> + for_each_present_cpu(cpu)
>>> {
>>> offset = t_info_first_offset + (cpu * pages);
>>> t_info->mfn_offset[cpu] = offset;
>>
>> Doesn't this go a little too far? Why would you allocate buffers for CPUs
>> which can never be brought online? There ought to be a middle ground,
>> where online-able CPUs have buffers allocated, but non-online-able ones
>> won't. On larger systems I guess the difference may be quite noticable.
>
> According to the comments in include/xen/cpumask.h cpu_present_map
> represents the populated cpus.
>
> I know that currently there is no support for onlining a parked cpu
> again, but I think having to think about Xentrace buffer allocation in
> case onlining of parked cpus is added would be a nearly 100% chance to
> introduce a bug.
>
> Xentrace is used for testing purposes only. So IMHO allocating some more
> memory is acceptable.
Are you fine with my reasoning or do you still want me to avoid buffer
allocation for offline cpus?
Juergen
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