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From: Christopher Lameter <cl@linux.com>
To: Leonardo Bras <leonardo@linux.ibm.com>
Cc: "Song Liu" <songliubraving@fb.com>,
	"Michal Hocko" <mhocko@suse.com>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	"Dmitry V. Levin" <ldv@altlinux.org>,
	"Keith Busch" <keith.busch@intel.com>,
	linux-mm@kvack.org, "Paul Mackerras" <paulus@samba.org>,
	"Christian Brauner" <christian.brauner@ubuntu.com>,
	"Ira Weiny" <ira.weiny@intel.com>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Elena Reshetova" <elena.reshetova@intel.com>,
	linux-arch@vger.kernel.org,
	"Santosh Sivaraj" <santosh@fossix.org>,
	"Davidlohr Bueso" <dave@stgolabs.net>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
	"Bartlomiej Zolnierkiewicz" <b.zolnierkie@samsung.com>,
	"Mike Rapoport" <rppt@linux.ibm.com>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"Mahesh Salgaonkar" <mahesh@linux.vnet.ibm.com>,
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	"Alexey Dobriyan" <adobriyan@gmail.com>,
	"Ingo Molnar" <mingo@kernel.org>,
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	"Ralph Campbell" <rcampbell@nvidia.com>,
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	"John Hubbard" <jhubbard@nvidia.com>,
	"Jesper Dangaard Brouer" <brouer@redhat.com>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>,
	kvm-ppc@vger.kernel.org, "Thomas Gleixner" <tglx@linutronix.de>,
	"Reza Arbab" <arbab@linux.ibm.com>,
	"Allison Randal" <allison@lohutok.net>,
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	linux-kernel@vger.kernel.org,
	"Logan Gunthorpe" <logang@deltatee.com>,
	"Souptick Joarder" <jrdr.linux@gmail.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	linuxppc-dev@lists.ozlabs.org, "Roman Gushchin" <guro@fb.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	"Al Viro" <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v5 02/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks
Date: Tue, 8 Oct 2019 17:43:10 +0000 (UTC)	[thread overview]
Message-ID: <alpine.DEB.2.21.1910081741460.2923@www.lameter.com> (raw)
In-Reply-To: <6e8877bff034603e75b35599797a39d9bc4840f1.camel@linux.ibm.com>

On Tue, 8 Oct 2019, Leonardo Bras wrote:

> > You are creating contention on a single exclusive cacheline. Doesnt this
> > defeat the whole purpose of the lockless page table walk? Use mmap_sem or
> > so should cause the same performance regression?
>
> Sorry, I did not understand that question.
> I mean, this is just a refcount and never causes a lock.

Locks also use atomic operations like a refcount increment. Both require
the cacheline to be in exclusive state. So the impact is very similar.


  reply	other threads:[~2019-10-08 17:43 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-03  1:33 [PATCH v5 00/11] Introduces new count-based method for tracking lockless pagetable walks Leonardo Bras
2019-10-03  1:33 ` [PATCH v5 01/11] asm-generic/pgtable: Adds generic functions to monitor lockless pgtable walks Leonardo Bras
2019-10-03  7:11   ` Peter Zijlstra
2019-10-03 11:51     ` Peter Zijlstra
2019-10-03 20:40       ` John Hubbard
2019-10-04 11:24         ` Peter Zijlstra
2019-10-03 21:24       ` Leonardo Bras
2019-10-04 11:28         ` Peter Zijlstra
2019-10-09 18:09           ` Leonardo Bras
2019-10-05  8:35       ` Aneesh Kumar K.V
2019-10-08 14:47         ` Kirill A. Shutemov
2019-10-03  1:33 ` [PATCH v5 02/11] powerpc/mm: Adds counting method " Leonardo Bras
2019-10-08 15:11   ` Christopher Lameter
2019-10-08 17:13     ` Leonardo Bras
2019-10-08 17:43       ` Christopher Lameter [this message]
2019-10-08 18:02         ` Leonardo Bras
2019-10-08 18:27           ` Christopher Lameter
2019-10-03  1:33 ` [PATCH v5 03/11] mm/gup: Applies counting method to monitor gup_pgd_range Leonardo Bras
2019-10-03  1:33 ` [PATCH v5 04/11] powerpc/mce_power: Applies counting method to monitor lockless pgtbl walks Leonardo Bras
2019-10-03  1:33 ` [PATCH v5 05/11] powerpc/perf: " Leonardo Bras
2019-10-03  1:33 ` [PATCH v5 06/11] powerpc/mm/book3s64/hash: " Leonardo Bras
2019-10-03  1:33 ` [PATCH v5 07/11] powerpc/kvm/e500: " Leonardo Bras
2019-10-03  1:33 ` [PATCH v5 08/11] powerpc/kvm/book3s_hv: " Leonardo Bras
2019-10-03  1:33 ` [PATCH v5 09/11] powerpc/kvm/book3s_64: " Leonardo Bras
2019-10-03  1:33 ` [PATCH v5 10/11] mm/Kconfig: Adds config option to track lockless pagetable walks Leonardo Bras
2019-10-03  2:08   ` Qian Cai
2019-10-03 19:04     ` Leonardo Bras
2019-10-03 19:08       ` Leonardo Bras
2019-10-03  7:44   ` Peter Zijlstra
2019-10-03 20:40     ` Leonardo Bras
2019-10-03  1:33 ` [PATCH v5 11/11] powerpc/mm/book3s64/pgtable: Uses counting method to skip serializing Leonardo Bras
2019-10-03  7:29 ` [PATCH v5 00/11] Introduces new count-based method for tracking lockless pagetable walks Peter Zijlstra
2019-10-03 20:36   ` Leonardo Bras
2019-10-03 20:49     ` John Hubbard
2019-10-03 21:38       ` Leonardo Bras
2019-10-04 11:42     ` Peter Zijlstra
2019-10-04 12:57       ` Peter Zijlstra

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