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[80.212.254.60]) by smtp.gmail.com with ESMTPSA id q21sm196923lfp.233.2021.06.24.04.21.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Jun 2021 04:21:53 -0700 (PDT) From: Odin Ugedal To: Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Sachin Sant , Naresh Kamboju Cc: Ingo Molnar , Juri Lelli , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , linux-kernel@vger.kernel.org, Odin Ugedal Subject: [PATCH] sched/fair: Ensure _sum and _avg values stay consistent Date: Thu, 24 Jun 2021 13:18:15 +0200 Message-Id: <20210624111815.57937-1-odin@uged.al> X-Mailer: git-send-email 2.32.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The _sum and _avg values are in general sync together with the PELT divider. They are however not always completely in perfect sync, resulting in situations where _sum gets to zero while _avg stays positive. Such situations are undesirable. This comes from the fact that PELT will increase period_contrib, also increasing the PELT divider, without updating _sum and _avg values to stay in perfect sync where (_sum == _avg * divider). However, such PELT change will never lower _sum, making it impossible to end up in a situation where _sum is zero and _avg is not. Therefore, we need to ensure that when subtracting load outside PELT, that when _sum is zero, _avg is also set to zero. This occurs when (_sum < _avg * divider), and the subtracted (_avg * divider) is bigger or equal to the current _sum, while the subtracted _avg is smaller than the current _avg. Reported-by: Sachin Sant Reported-by: Naresh Kamboju Signed-off-by: Odin Ugedal --- Reports and discussion can be found here: https://lore.kernel.org/lkml/2ED1BDF5-BC0C-47CD-8F33-9A46C738F8CF@linux.vnet.ibm.com/ https://lore.kernel.org/lkml/CA+G9fYsMXELmjGUzw4SY1bghTYz_PeR2diM6dRp2J37bBZzMSA@mail.gmail.com/ kernel/sched/fair.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index bfaa6e1f6067..def48bc2e90b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3688,15 +3688,15 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) r = removed_load; sub_positive(&sa->load_avg, r); - sub_positive(&sa->load_sum, r * divider); + sa->load_sum = sa->load_avg * divider; r = removed_util; sub_positive(&sa->util_avg, r); - sub_positive(&sa->util_sum, r * divider); + sa->util_sum = sa->util_avg * divider; r = removed_runnable; sub_positive(&sa->runnable_avg, r); - sub_positive(&sa->runnable_sum, r * divider); + sa->runnable_sum = sa->runnable_avg * divider; /* * removed_runnable is the unweighted version of removed_load so we -- 2.32.0