Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190218165620.383905466@infradead.org> <CAHk-=wh32Zgp+bN7G1KH7SuCiY1YSJ41Y-_eWpfWubGjqq2_dw@mail.gmail.com>
 <20190218204020.GV32494@hirez.programming.kicks-ass.net>
In-Reply-To: <20190218204020.GV32494@hirez.programming.kicks-ass.net>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 18 Feb 2019 16:29:56 -0800
Message-ID: <CAHk-=whVrNomWXRmCjnBJkosiwiGXz5pYb63aXy=nSPGjvc-1g@mail.gmail.com>
Subject: Re: [RFC][PATCH 00/16] sched: Core scheduling
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paul Turner <pjt@google.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        subhra.mazumdar@oracle.com,
        =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= <fweisbec@gmail.com>,
        Kees Cook <keescook@chromium.org>, kerrnel@google.com
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Feb 18, 2019 at 12:40 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> If there were close to no VMEXITs, it beat smt=off, if there were lots
> of VMEXITs it was far far worse. Supposedly hosting people try their
> very bestest to have no VMEXITs so it mostly works for them (with the
> obvious exception of single VCPU guests).
>
> It's just that people have been bugging me for this crap; and I figure
> I'd post it now that it's not exploding anymore and let others have at.

The patches didn't look disgusting to me, but I admittedly just
scanned through them quickly.

Are there downsides (maintenance and/or performance) when core
scheduling _isn't_ enabled? I guess if it's not a maintenance or
performance nightmare when off, it's ok to just give people the
option.

That all assumes that it works at all for the people who are clamoring
for this feature, but I guess they can run some loads on it
eventually. It's a holiday in the US right now ("Presidents' Day"),
but maybe we can get some numebrs this week?

                Linus