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Message-ID: <20160829164809.GW10153@twins.programming.kicks-ass.net>
Date: Mon, 29 Aug 2016 18:48:09 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Gilad Ben Yossef <giladb@...lanox.com>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Christoph Lameter <cl@...ux.com>,
Viresh Kumar <viresh.kumar@...aro.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Andy Lutomirski <luto@...capital.net>,
Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
linux-doc@...r.kernel.org, linux-api@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v15 04/13] task_isolation: add initial support
On Mon, Aug 29, 2016 at 12:40:32PM -0400, Chris Metcalf wrote:
> On 8/29/2016 12:33 PM, Peter Zijlstra wrote:
> >On Tue, Aug 16, 2016 at 05:19:27PM -0400, Chris Metcalf wrote:
> >>+ /*
> >>+ * Request rescheduling unless we are in full dynticks mode.
> >>+ * We would eventually get pre-empted without this, and if
> >>+ * there's another task waiting, it would run; but by
> >>+ * explicitly requesting the reschedule, we may reduce the
> >>+ * latency. We could directly call schedule() here as well,
> >>+ * but since our caller is the standard place where schedule()
> >>+ * is called, we defer to the caller.
> >>+ *
> >>+ * A more substantive approach here would be to use a struct
> >>+ * completion here explicitly, and complete it when we shut
> >>+ * down dynticks, but since we presumably have nothing better
> >>+ * to do on this core anyway, just spinning seems plausible.
> >>+ */
> >>+ if (!tick_nohz_tick_stopped())
> >>+ set_tsk_need_resched(current);
> >This is broken.. and it would be really good if you don't actually need
> >to do this.
>
> Can you elaborate?
Naked use of TIF_NEED_RESCHED like this is busted. There is more state
that needs to be poked to keep things consistent / working.
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