linux-kernel - Re: [PATCH v9 00/13] support "task_isolation" mode for nohz

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Date:	Tue, 12 Jan 2016 12:49:46 -0500
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Will Deacon <will.deacon@....com>
CC:	Gilad Ben Yossef <giladb@...hip.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.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>,
	Andy Lutomirski <luto@...capital.net>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	<linux-doc@...r.kernel.org>, <linux-api@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v9 00/13] support "task_isolation" mode for nohz_full

(Adding Mark to cc's)

On 01/12/2016 05:07 AM, Will Deacon wrote:
> On Mon, Jan 11, 2016 at 04:15:50PM -0500, Chris Metcalf wrote:
>> Ping!  There has been no substantive feedback to this version of
>> the patch in the week since I posted it, which optimistically suggests
>> to me that people may be satisfied with it.  If that's true, Frederic,
>> I assume this would be pulled into your tree?
>>
>> I have slightly updated the v9 patch series since this posting:
>>
>> [...]
>>
>> - Incorporated Mark Rutland's changes to convert arm64
>>    assembly to C code instead of using my own version.
> Please avoid queuing these patches -- the first is already in the arm64
> queue for 4.5 and the second was found to introduce a substantial
> performance regression on the syscall entry/exit path. I think Mark had
> an updated version to address that, so it would be easier not to have
> an old version sitting in some other queue!

I am not formally queueing them anywhere (like linux-next), though
now that you mention it, that's a pretty good idea - I'll talk to Steven
about that, assuming this merge window closes without the task
isolation stuff going in.

In the arch/tile code, we load the thread_info_flags and test them
against a bitmask before we call into C code, to avoid the various
overheads involved in the C path.  Perhaps that same strategy is all
that's needed for the arm64 code?  Hopefully you can get that
code merged up during the 4.5 window so I can use it as the new
baseline for the task isolation stuff.

Thanks!

-- 
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com