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

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Message-ID: <20160811091347.GA10990@gmail.com>
Date:	Thu, 11 Aug 2016 11:13:47 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Aaron Lu <aaron.lu@...el.com>
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


* 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:

  3dec0ba0be6a ("mm/rmap: share the i_mmap_rwsem")

I have fixed this in the changelog.

Thanks,

	Ingo