On 9/8/25 09:26, Daniel Wagner wrote:
On Mon, Sep 08, 2025 at 08:13:31AM +0200, Hannes Reinecke wrote:
const struct cpumask *blk_mq_online_queue_affinity(void)
{
+ if (housekeeping_enabled(HK_TYPE_IO_QUEUE)) {
+ cpumask_and(&blk_hk_online_mask, cpu_online_mask,
+ housekeeping_cpumask(HK_TYPE_IO_QUEUE));
+ return &blk_hk_online_mask;
Can you explain the use of 'blk_hk_online_mask'?
Why is a static variable?
The blk_mq_*_queue_affinity helpers return a const struct cpumask *, the
caller doesn't need to free the return value. Because cpumask_and needs
store its result somewhere, I opted for the global static variable.
To my untrained eye it's being recalculated every time one calls
this function. And only the first invocation run on an empty mask,
all subsequent ones see a populated mask.
The cpu_online_mask might change over time, it's not a static bitmap.
Thus it's necessary to update the blk_hk_online_mask. Doing some sort of
caching is certainly possible. Given that we have plenty of cpumask
logic operation in the cpu_group_evenly code path later, I am not so
sure this really makes a huge difference.
Oh, that's okay. I'm perfectly fine to update the cpumask on every call.
What makes me wonder is the initialisation of blk_hk_online_mask;
it's zeroed _at boot_, and then all we do is calling cpumask_and()
for every invocation. So the mask will only increase in scope,
and never decrease.
Wouldn't it be better to call 'cpumask_zero' before 'cpumask_and'?
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
h...@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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