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From: Ingo Molnar <mingo@kernel.org>
To: linux-kernel@vger.kernel.org, linux-mm@kvack.org
Cc: Andy Lutomirski <luto@amacapital.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	Brian Gerst <brgerst@gmail.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Waiman Long <Waiman.Long@hp.com>
Subject: Re: [RFC PATCH 00/12] x86/mm: Implement lockless pgd_alloc()/pgd_free()
Date: Thu, 11 Jun 2015 16:13:53 +0200	[thread overview]
Message-ID: <20150611141353.GA9447@gmail.com> (raw)
In-Reply-To: <1434031637-9091-1-git-send-email-mingo@kernel.org>


[ I fat-fingered the linux-mm Cc:, so every reply will bounce on that,
  sorry about that  :-/ Fixed it in this mail's Cc: list. ]

* Ingo Molnar <mingo@kernel.org> wrote:

> Waiman Long reported 'pgd_lock' contention on high CPU count systems and 
> proposed moving pgd_lock on a separate cacheline to eliminate false sharing and 
> to reduce some of the lock bouncing overhead.

So 'pgd_lock' is a global lock, used for every new task creation:

arch/x86/mm/fault.c:DEFINE_SPINLOCK(pgd_lock);

which with a sufficiently high CPU count starts to hurt.

Thanks,

	Ingo

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WARNING: multiple messages have this Message-ID (diff)
From: Ingo Molnar <mingo@kernel.org>
To: linux-kernel@vger.kernel.org, linux-mm@kvack.org
Cc: Andy Lutomirski <luto@amacapital.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	Brian Gerst <brgerst@gmail.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Waiman Long <Waiman.Long@hp.com>
Subject: Re: [RFC PATCH 00/12] x86/mm: Implement lockless pgd_alloc()/pgd_free()
Date: Thu, 11 Jun 2015 16:13:53 +0200	[thread overview]
Message-ID: <20150611141353.GA9447@gmail.com> (raw)
In-Reply-To: <1434031637-9091-1-git-send-email-mingo@kernel.org>


[ I fat-fingered the linux-mm Cc:, so every reply will bounce on that,
  sorry about that  :-/ Fixed it in this mail's Cc: list. ]

* Ingo Molnar <mingo@kernel.org> wrote:

> Waiman Long reported 'pgd_lock' contention on high CPU count systems and 
> proposed moving pgd_lock on a separate cacheline to eliminate false sharing and 
> to reduce some of the lock bouncing overhead.

So 'pgd_lock' is a global lock, used for every new task creation:

arch/x86/mm/fault.c:DEFINE_SPINLOCK(pgd_lock);

which with a sufficiently high CPU count starts to hurt.

Thanks,

	Ingo

  parent reply	other threads:[~2015-06-11 14:14 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-06-11 14:07 [RFC PATCH 00/12] x86/mm: Implement lockless pgd_alloc()/pgd_free() Ingo Molnar
2015-06-11 14:07 ` [PATCH 01/12] x86/mm/pat: Don't free PGD entries on memory unmap Ingo Molnar
2015-06-11 14:07 ` [PATCH 02/12] x86/mm/hotplug: Remove pgd_list use from the memory hotplug code Ingo Molnar
2015-06-12 22:22   ` Oleg Nesterov
2015-06-12 22:48   ` Waiman Long
2015-06-13  7:46     ` Ingo Molnar
2015-06-12 23:15   ` Oleg Nesterov
2015-06-13  7:48     ` Ingo Molnar
2015-06-11 14:07 ` [PATCH 03/12] x86/mm/hotplug: Don't remove PGD entries in remove_pagetable() Ingo Molnar
2015-06-11 14:07 ` [PATCH 04/12] x86/mm/hotplug: Simplify sync_global_pgds() Ingo Molnar
2015-06-12 22:28   ` Oleg Nesterov
2015-06-13  7:51     ` Ingo Molnar
2015-06-11 14:07 ` [PATCH 05/12] mm: Introduce arch_pgd_init_late() Ingo Molnar
2015-06-11 18:23   ` Andrew Morton
2015-06-12  8:16     ` Ingo Molnar
2015-06-12 21:12   ` Oleg Nesterov
2015-06-13  6:54     ` Ingo Molnar
2015-06-11 14:07 ` [PATCH 06/12] x86/mm: Enable and use the arch_pgd_init_late() method Ingo Molnar
2015-06-11 20:04   ` Boris Ostrovsky
2015-06-12  8:19     ` Ingo Molnar
2015-06-12 22:50   ` Oleg Nesterov
2015-06-12 22:57     ` Oleg Nesterov
2015-06-13  6:49       ` Ingo Molnar
2015-06-13  6:47     ` Ingo Molnar
2015-06-13  6:52       ` Ingo Molnar
2015-06-13 17:45         ` Oleg Nesterov
2015-06-14  8:13           ` Ingo Molnar
2015-06-14 20:54             ` Oleg Nesterov
2015-06-14 22:10               ` Oleg Nesterov
2015-06-11 14:07 ` [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from the Xen guest code Ingo Molnar
2015-06-11 20:37   ` Linus Torvalds
2015-06-11 20:41     ` Linus Torvalds
2015-06-12  7:23       ` Ingo Molnar
     [not found]         ` <CA+55aFxXM=DN32JqNmJ=JoMum5OPnsRohCry-=2T=LabX2hzVQ@mail.gmail.com>
2015-06-12  8:04           ` Ingo Molnar
2015-06-12 20:38             ` Oleg Nesterov
2015-06-12 20:53               ` Oleg Nesterov
2015-06-12 22:30                 ` Boris Ostrovsky
2015-06-12 23:36                   ` Oleg Nesterov
2015-06-13  7:26               ` Ingo Molnar
2015-06-13 18:00                 ` Oleg Nesterov
2015-06-11 14:07 ` [PATCH 08/12] x86/mm: Remove pgd_list use from vmalloc_sync_all() Ingo Molnar
2015-06-11 15:04   ` Andy Lutomirski
2015-06-11 15:49     ` Ingo Molnar
2015-06-11 16:10       ` Andy Lutomirski
2015-06-11 14:07 ` [PATCH 09/12] x86/mm/pat/32: Remove pgd_list use from the PAT code Ingo Molnar
2015-06-11 14:07 ` [PATCH 10/12] x86/mm: Make pgd_alloc()/pgd_free() lockless Ingo Molnar
2015-06-11 14:07 ` [PATCH 11/12] x86/mm: Remove pgd_list leftovers Ingo Molnar
2015-06-11 14:07 ` [PATCH 12/12] x86/mm: Simplify pgd_alloc() Ingo Molnar
2015-06-11 14:13 ` Ingo Molnar [this message]
2015-06-11 14:13   ` [RFC PATCH 00/12] x86/mm: Implement lockless pgd_alloc()/pgd_free() Ingo Molnar
2015-06-11 16:46 ` H. Peter Anvin

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