linux-kernel - Re: [PATCH] x86/irq: do not substract irq_tlb_count from irq_call

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Message-ID: <b750f917-3049-7bb9-11b6-0d9980f8f1e6@intel.com>
Date:	Thu, 11 Aug 2016 17:16:49 +0800
From:	Aaron Lu <aaron.lu@...el.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Alex Shi <alex.shi@...aro.org>,
	Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Huang Ying <ying.huang@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/irq: do not substract irq_tlb_count from
 irq_call_count

On 08/11/2016 05:13 PM, Ingo Molnar wrote:
> 
> * Aaron Lu <aaron.lu@...el.com> wrote:
> 
>> This is found by LKP's cyclic performance regression tracking recently
>> with the vm-scalability test suite. I have bisected to commit
>> 0a7ce4b5a632 ("mm/rmap: share the i_mmap_rwsem"). This commit didn't do
>> anything wrong but revealed the irq_call_count problem. IIUC, the commit
>> makes rwc->remap_one in rmap_walk_file concurrent with multiple threads.
>> When remap_one is try_to_unmap_one, then multiple threads could queue
>> flush tlb to the same CPU but only one IPI will be sent.
> 
> Note, for some reason the commit ID you used is wrong, the real one is:

Oops, I looked at a test branch where I cherry-picked that commit, sorry.

> 
>   3dec0ba0be6a ("mm/rmap: share the i_mmap_rwsem")
> 
> I have fixed this in the changelog.

Thanks!