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[61.68.227.232]) by smtp.gmail.com with ESMTPSA id g85sm2868683pfb.4.2020.11.25.16.11.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Nov 2020 16:11:31 -0800 (PST) Date: Thu, 26 Nov 2020 11:11:28 +1100 From: Balbir Singh To: Peter Zijlstra Cc: "Joel Fernandes (Google)" , Nishanth Aravamudan , Julien Desfossez , Tim Chen , Vineeth Pillai , Aaron Lu , Aubrey Li , tglx@linutronix.de, linux-kernel@vger.kernel.org, mingo@kernel.org, torvalds@linux-foundation.org, fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com, Phil Auld , Valentin Schneider , Mel Gorman , Pawan Gupta , Paolo Bonzini , vineeth@bitbyteword.org, Chen Yu , Christian Brauner , Agata Gruza , Antonio Gomez Iglesias , graf@amazon.com, konrad.wilk@oracle.com, dfaggioli@suse.com, pjt@google.com, rostedt@goodmis.org, derkling@google.com, benbjiang@tencent.com, Alexandre Chartre , James.Bottomley@hansenpartnership.com, OWeisse@umich.edu, Dhaval Giani , Junaid Shahid , jsbarnes@google.com, chris.hyser@oracle.com, Ben Segall , Josh Don , Hao Luo , Tom Lendacky , Aubrey Li , "Paul E. McKenney" , Tim Chen Subject: Re: [PATCH -tip 31/32] sched: Add a coresched command line option Message-ID: <20201126001128.GF163610@balbir-desktop> References: <20201117232003.3580179-1-joel@joelfernandes.org> <20201117232003.3580179-32-joel@joelfernandes.org> <20201125134537.GA2414@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201125134537.GA2414@hirez.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 25, 2020 at 02:45:37PM +0100, Peter Zijlstra wrote: > On Tue, Nov 17, 2020 at 06:20:01PM -0500, Joel Fernandes (Google) wrote: > > Some hardware such as certain AMD variants don't have cross-HT MDS/L1TF > > issues. Detect this and don't enable core scheduling as it can > > needlessly slow those device down. > > > > However, some users may want core scheduling even if the hardware is > > secure. To support them, add a coresched= option which defaults to > > 'secure' and can be overridden to 'on' if the user wants to enable > > coresched even if the HW is not vulnerable. 'off' would disable > > core scheduling in any case. > > This is all sorts of wrong, and the reason is because you hard-coded > that stupid policy. > > Core scheduling should always be available on SMT (provided you did that > CONFIG_ thing). Even on AMD systems RT tasks might want to claim the > core exclusively. Agreed, specifically if we need to have special cgroup tag/association to enable it. Balbir Singh.