From: Leonardo Bras <leonardo@linux.ibm.com>
To: Christopher Lameter <cl@linux.com>
Cc: Song Liu <songliubraving@fb.com>, Michal Hocko <mhocko@suse.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
"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>, Ingo Molnar <mingo@kernel.org>,
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>,
Jann Horn <jannh@google.com>, Mike Rapoport <rppt@linux.ibm.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
Allison Randal <allison@lohutok.net>,
Jesper Dangaard Brouer <brouer@redhat.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Andrea
Subject: Re: [PATCH v5 02/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks
Date: Tue, 08 Oct 2019 14:13:55 -0300 [thread overview]
Message-ID: <6e8877bff034603e75b35599797a39d9bc4840f1.camel@linux.ibm.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1910081509070.1734@www.lameter.com>
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On Tue, 2019-10-08 at 15:11 +0000, Christopher Lameter wrote:
>
> On Wed, 2 Oct 2019, Leonardo Bras wrote:
>
> > +
> > +inline unsigned long __begin_lockless_pgtbl_walk(struct mm_struct *mm,
> > + bool disable_irq)
> > +{
> > + unsigned long irq_mask = 0;
> > +
> > + if (IS_ENABLED(CONFIG_LOCKLESS_PAGE_TABLE_WALK_TRACKING))
> > + atomic_inc(&mm->lockless_pgtbl_walkers);
> > +
>
> 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.
FYI: This function was updated as following, and will be in v6:
#ifdef CONFIG_LOCKLESS_PAGE_TABLE_WALK_TRACKING
atomic_inc(&mm->lockless_pgtbl_walkers);
#endif
smp_mb();
IS_ENABLED doesnt work fine if CONFIG_LOCKLESS_PAGE_TABLE_WALK_TRACKING
is not defined, causing an error: the mm member lockless_pgtbl_walkers
doesn't exist.
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next prev parent reply other threads:[~2019-10-08 17:13 UTC|newest]
Thread overview: 45+ 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
2019-10-03 21:24 ` Leonardo Bras
2019-10-04 11:28 ` Peter Zijlstra
2019-10-04 11:28 ` Peter Zijlstra
2019-10-09 18:09 ` Leonardo Bras
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 [this message]
2019-10-08 17:43 ` Christopher Lameter
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 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 20:36 ` Leonardo Bras
2019-10-03 20:49 ` John Hubbard
2019-10-03 21:38 ` Leonardo Bras
2019-10-03 21:38 ` Leonardo Bras
2019-10-04 11:42 ` Peter Zijlstra
2019-10-04 11:42 ` Peter Zijlstra
2019-10-04 12:57 ` Peter Zijlstra
2019-10-04 12:57 ` Peter Zijlstra
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