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.
Juergen
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