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[216.228.125.128]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2f447883b17sm31228610a91.40.2025.01.04.20.00.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 04 Jan 2025 20:00:13 -0800 (PST) Date: Sat, 4 Jan 2025 20:00:10 -0800 From: Yury Norov To: Andrea Righi Cc: Tejun Heo , David Vernet , Changwoo Min , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched_ext: idle: small CPU iteration refactoring Message-ID: References: <20250104090009.331193-1-arighi@nvidia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250104090009.331193-1-arighi@nvidia.com> On Sat, Jan 04, 2025 at 10:00:09AM +0100, Andrea Righi wrote: > loop to check if all SMT CPUs are idle with > cpumask_subset(). This simplifies the code and slightly improves > efficiency, while preserving the original behavior. In my experience, replacing iterator with a dedicated function makes you 400-500 times faster. So 'slightly' sounds like an understatement here. > Note that idle_masks.smt handling remains racy, which is acceptable as > it serves as an optimization and is self-correcting. > > Suggested-by: Yury Norov > Signed-off-by: Andrea Righi Reviewed-by: Yury Norov > --- > kernel/sched/ext.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c > index 926579624c41..0ce116e0f67c 100644 > --- a/kernel/sched/ext.c > +++ b/kernel/sched/ext.c > @@ -3671,10 +3671,8 @@ void __scx_update_idle(struct rq *rq, bool idle) > * idle_masks.smt handling is racy but that's fine as > * it's only for optimization and self-correcting. > */ > - for_each_cpu(cpu, smt) { > - if (!cpumask_test_cpu(cpu, idle_masks.cpu)) > - return; > - } > + if (!cpumask_subset(smt, idle_masks.cpu)) > + return; > cpumask_or(idle_masks.smt, idle_masks.smt, smt); > } else { > cpumask_andnot(idle_masks.smt, idle_masks.smt, smt); > -- > 2.47.1 > > From yury