linux-kernel - Re: [PATCH v4 4/4] KVM: selftests: Run dirty_log_perf

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Date:   Thu, 6 Oct 2022 20:26:57 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vipin Sharma <vipinsh@...gle.com>
Cc:     pbonzini@...hat.com, dmatlack@...gle.com, andrew.jones@...ux.dev,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/4] KVM: selftests: Run dirty_log_perf_test on
 specific CPUs

On Thu, Oct 06, 2022, Sean Christopherson wrote:
> On Thu, Oct 06, 2022, Vipin Sharma wrote:
> > +{
> > +	cpu_set_t cpuset;
> > +	int err;
> > +
> > +	CPU_ZERO(&cpuset);
> > +	CPU_SET(pcpu, &cpuset);
> 
> To save user pain:
> 
> 	r = sched_getaffinity(0, sizeof(allowed_mask), &allowed_mask);
> 	TEST_ASSERT(!r, "sched_getaffinity failed, errno = %d (%s)", errno,
> 		    strerror(errno));

Forgot TEST_ASSERT() already provides errno, this can just be:

	TEST_ASSERT(!r, "sched_getaffinity() failed");

> 
> 	TEST_ASSERT(CPU_ISSET(pcpu, &allowed_mask),
> 		    "Task '%d' not allowed to run on pCPU '%d'\n");
> 
> 	CPU_ZERO(&allowed_mask);
> 	CPU_SET(cpu, &allowed_mask);
> 
> that way the user will get an explicit error message if they try to pin a vCPU/task
> that has already been affined by something else.  And then, in theory,
> sched_setaffinity() should never fail.
> 
> Or you could have two cpu_set_t objects and use CPU_AND(), but that seems
> unnecessarily complex.
> 
> > +	err = sched_setaffinity(0, sizeof(cpu_set_t), &cpuset);
> > +	TEST_ASSERT(err == 0, "sched_setaffinity() errored out for pcpu: %d\n", pcpu);
> 
> !err is the preferred style, though I vote to use "r" instead of "err".  And print
> the errno so that the user can debug.

As above, ignore the last, forgot TEST_ASSERT() provides errno.

> 
> 	r = sched_setaffinity(0, sizeof(allowed_mask), &allowed_mask);
> 	TEST_ASSERT(!r, "sched_setaffinity failed, errno = %d (%s)",
> 		    errno, strerror(errno));