From:   Daniel Jordan <daniel.m.jordan@oracle.com>
To:     Alexander Duyck <alexanderduyck@fb.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ben Segall <bsegall@google.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ingo Molnar <mingo@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Michal Hocko <mhocko@suse.com>, Nico Pache <npache@redhat.com>,
        Pasha Tatashin <pasha.tatashin@soleen.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Steffen Klassert <steffen.klassert@secunet.com>,
        Steve Sistare <steven.sistare@oracle.com>,
        Tejun Heo <tj@kernel.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Vincent Guittot <vincent.guittot@linaro.org>
Cc:     linux-mm@kvack.org, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
        Daniel Jordan <daniel.m.jordan@oracle.com>
Subject: [RFC 10/16] padata: Helpers should respect main thread's CPU affinity
Date:   Wed,  5 Jan 2022 19:46:50 -0500
Message-Id: <20220106004656.126790-11-daniel.m.jordan@oracle.com>
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Helper threads should run only on the CPUs allowed by the main thread to
honor its CPU affinity.  Similarly, cap the number of helpers started to
the number of CPUs allowed by the main thread's cpumask to avoid
flooding that subset of CPUs.

Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
---
 kernel/padata.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index 00509c83e356..0f4002ed1518 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -571,6 +571,7 @@ int padata_do_multithreaded_job(struct padata_mt_job *job,
 	/* Ensure at least one thread when size < min_chunk. */
 	nworks = max(job->size / job->min_chunk, 1ul);
 	nworks = min(nworks, job->max_threads);
+	nworks = min(nworks, current->nr_cpus_allowed);
 
 	if (nworks == 1) {
 		/* Single thread, no coordination needed, cut to the chase. */
@@ -607,10 +608,12 @@ int padata_do_multithreaded_job(struct padata_mt_job *job,
 
 		pw->pw_data = &ps;
 		task = kthread_create(padata_mt_helper, pw, "padata");
-		if (IS_ERR(task))
+		if (IS_ERR(task)) {
 			--ps.nworks;
-		else
+		} else {
+			kthread_bind_mask(task, current->cpus_ptr);
 			wake_up_process(task);
+		}
 	}
 
 	/* Use the current task, which saves starting a kthread. */
-- 
2.34.1