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[209.85.220.65]) by mx.google.com with SMTPS id f2sor4932221ywa.0.2019.01.29.15.36.19 for (Google Transport Security); Tue, 29 Jan 2019 15:36:19 -0800 (PST) Received-SPF: pass (google.com: domain of hannes@cmpxchg.org designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@cmpxchg-org.20150623.gappssmtp.com header.s=20150623 header.b=JnOTWShy; spf=pass (google.com: domain of hannes@cmpxchg.org designates 209.85.220.65 as permitted sender) smtp.mailfrom=hannes@cmpxchg.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=cmpxchg.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=ypcjhC5gLgv1najtmqf3KGwBGuKlXgrvvho14o6HPq4=; b=JnOTWShy8zOoZyip47uhC8ph1M4XcBA2QNn/g34BScolFhs1qAn5yHiIAiYqNKjwHY nmCc9DcEdq5jBZ8RAhFB/5J2py2kKU47cVjPJ+KWp/bwqEEe0RAxd5fOzNg1SVcsfEqK v8j/SDr9HWejcaQ0n9k7CG7A6XP2mgL6JkcmWaE6BKnZLlr51syPc9bw0yQBJnsu/rUZ EjMOSfq0hVZLVhf78Ieu+Vt168ODqC3uhSZlf9yg3mEfuw3Kwrh6XDmMMtkLHpSDDYiX n+K+K7XRC38sbnnXxoPxYPA1ZiZ/17uZZd6rHcaGaqYcNDdPG/OsjrYY6EEKOBDiDuWO bICA== X-Google-Smtp-Source: ALg8bN6PRN1HYwkcGXaRrY0s20nXRdjPrEH7n5y8QSD0tg5DA7sqfugxO+FQ+zN8x44L+qcnQSxumA== X-Received: by 2002:a81:6257:: with SMTP id w84mr27686832ywb.273.1548804979275; Tue, 29 Jan 2019 15:36:19 -0800 (PST) Received: from localhost ([2620:10d:c091:200::4:1d25]) by smtp.gmail.com with ESMTPSA id j12sm16757805ywk.43.2019.01.29.15.36.18 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 29 Jan 2019 15:36:18 -0800 (PST) From: Johannes Weiner To: Andrew Morton Cc: Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] psi: clarify the Kconfig text for the default-disable option Date: Tue, 29 Jan 2019 18:36:17 -0500 Message-Id: <20190129233617.16767-1-hannes@cmpxchg.org> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP The current help text caused some confusion in online forums about whether or not to default-enable or default-disable psi in vendor kernels. This is because it doesn't communicate the reason for why we made this setting configurable in the first place: that the overhead is non-zero in an artificial scheduler stress test. Since this isn't representative of real workloads, and the effect was not measurable in scheduler-heavy real world applications such as the webservers and memcache installations at Facebook, it's fair to point out that this is a pretty cautious option to select. Signed-off-by: Johannes Weiner --- init/Kconfig | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/init/Kconfig b/init/Kconfig index 513fa544a134..ad3381e57402 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -512,6 +512,17 @@ config PSI_DEFAULT_DISABLED per default but can be enabled through passing psi=1 on the kernel commandline during boot. + This feature adds some code to the task wakeup and sleep + paths of the scheduler. The overhead is too low to affect + common scheduling-intense workloads in practice (such as + webservers, memcache), but it does show up in artificial + scheduler stress tests, such as hackbench. + + If you are paranoid and not sure what the kernel will be + used for, say Y. + + Say N if unsure. + endmenu # "CPU/Task time and stats accounting" config CPU_ISOLATION