Re: [PATCH v3 00/20] Speculative page faults

From: Laurent Dufour <ldufour@linux.vnet.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	kirill@shutemov.name, Andi Kleen <ak@linux.intel.com>,
	Michal Hocko <mhocko@kernel.org>,
	dave@stgolabs.net, Jan Kara <jack@suse.cz>,
	Matthew Wilcox <willy@infradead.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Paul Mackerras <paulus@samba.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Will Deacon <will.deacon@arm.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	haren@linux.vnet.ibm.com,
	Anshuman Khandual <khandual@linux.vnet.ibm.com>,
	npiggin@gmail.com, bsingharora@gmail.com,
	Tim Chen <tim.c.chen@linux.intel.com>,
	linuxppc-dev@lists.ozlabs.org, "x86@kernel.org" <x86@kernel.org>
Subject: Re: [PATCH v3 00/20] Speculative page faults
Date: Thu, 28 Sep 2017 14:29:02 +0200	[thread overview]
Message-ID: <924a79af-6d7a-316a-1eee-3aebbfd4addf@linux.vnet.ibm.com> (raw)
In-Reply-To: <20170925163443.260d6092160ec704e2b04653@linux-foundation.org>

Hi Andrew,

On 26/09/2017 01:34, Andrew Morton wrote:
> On Mon, 25 Sep 2017 09:27:43 -0700 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> 
>> On Mon, Sep 18, 2017 at 12:15 AM, Laurent Dufour
>> <ldufour@linux.vnet.ibm.com> wrote:
>>> Despite the unprovable lockdep warning raised by Sergey, I didn't get any
>>> feedback on this series.
>>>
>>> Is there a chance to get it moved upstream ?
>>
>> what is the status ?
>> We're eagerly looking forward for this set to land,
>> since we have several use cases for tracing that
>> will build on top of this set as discussed at Plumbers.
> 
> There has been sadly little review and testing so far :(
> 
> I'll be taking a close look at it all over the next couple of weeks.
> 
> One terribly important thing (especially for a patchset this large and
> intrusive) is the rationale for merging it: the justification, usually
> in the form of end-user benefit.
> 
> Laurent's [0/n] provides some nice-looking performance benefits for
> workloads which are chosen to show performance benefits(!) but, alas,
> no quantitative testing results for workloads which we may suspect will
> be harmed by the changes(?).  Even things as simple as impact upon
> single-threaded pagefault-intensive workloads and its effect upon
> CONFIG_SMP=n .text size?

I forgot to mention in my previous email the impact on the .text section.

Here are the metrics I got :

.text size	UP		SMP		Delta
4.13-mmotm	8444201		8964137		6.16%
'' +spf		8452041		8971929		6.15%
	Delta	0.09%		0.09%	

No major impact as you could see.

Thanks,
Laurent

> If you have additional usecases then please, spell them out for us in
> full detail so we can better understand the benefits which this
> patchset provides.
> 