From: Linus Torvalds <torvalds@linux-foundation.org>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: Andrey Konovalov <andreyknvl@google.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Rich Felker <dalias@libc.org>,
"David S. Miller" <davem@davemloft.net>,
Christoph Hellwig <hch@lst.de>, James Hogan <jhogan@kernel.org>,
Khalid Aziz <khalid.aziz@oracle.com>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
linux-mips@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
linuxppc-dev@lists.ozlabs.org,
Linux-sh list <linux-sh@vger.kernel.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Paul Burton <paul.burton@mips.com>,
Paul Mackerras <paulus@samba.org>,
sparclinux@vger.kernel.org,
"the arch/x86 maintainers" <x86@kernel.org>,
Yoshinori Sato <ysato@users.sourceforge.jp>
Subject: Re: [PATCH 16/16] mm: pass get_user_pages_fast iterator arguments in a structure
Date: Thu, 20 Jun 2019 10:21:46 -0700 [thread overview]
Message-ID: <CAHk-=wh46y3x5O0HkR=R4ETh6e5pDCrEsJ94CtC0fyQiYYAf6A@mail.gmail.com> (raw)
In-Reply-To: <1561032202.0qfct43s2c.astroid@bobo.none>
On Thu, Jun 20, 2019 at 5:19 AM Nicholas Piggin <npiggin@gmail.com> wrote:
>
> The processor aliasing problem happens because the struct will
> be initialised with stores using one base register (e.g., stack
> register), and then same memory is loaded using a different
> register (e.g., parameter register).
Hmm. Honestly, I've never seen anything like that in any kernel profiles.
Compared to the problems I _do_ see (which is usually the obvious
cache misses, and locking), it must either be in the noise or it's
some problem specific to whatever CPU you are doing performance work
on?
I've occasionally seen pipeline hiccups in profiles, but it's usually
been either some serious glass jaw of the core, or it's been something
really stupid we did (or occasionally that the compiler did: one in
particular I remember was how there was a time when gcc would narrow
stores when it could, so if you set a bit in a word, it would do it
with a byte store, and then when you read the whole word afterwards
you'd get a major pipeline stall and it happened to show up in some
really hot paths).
Linus
next prev parent reply other threads:[~2019-06-20 17:22 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-11 14:40 switch the remaining architectures to use generic GUP v3 Christoph Hellwig
2019-06-11 14:40 ` [PATCH 01/16] mm: use untagged_addr() for get_user_pages_fast addresses Christoph Hellwig
2019-06-11 19:22 ` Khalid Aziz
2019-06-21 13:16 ` Jason Gunthorpe
2019-06-21 13:39 ` Jason Gunthorpe
2019-06-21 15:35 ` Khalid Aziz
2019-06-21 15:54 ` Jason Gunthorpe
2019-06-25 7:41 ` Christoph Hellwig
2019-06-25 7:43 ` Christoph Hellwig
2019-06-11 14:40 ` [PATCH 02/16] mm: simplify gup_fast_permitted Christoph Hellwig
2019-06-21 13:40 ` Jason Gunthorpe
2019-06-11 14:40 ` [PATCH 03/16] mm: lift the x86_32 PAE version of gup_get_pte to common code Christoph Hellwig
2019-06-21 13:45 ` Jason Gunthorpe
2019-06-11 14:40 ` [PATCH 04/16] MIPS: use the generic get_user_pages_fast code Christoph Hellwig
2019-06-21 14:05 ` Jason Gunthorpe
2019-06-25 7:46 ` Christoph Hellwig
2019-06-11 14:40 ` [PATCH 05/16] sh: add the missing pud_page definition Christoph Hellwig
2019-06-11 14:40 ` [PATCH 06/16] sh: use the generic get_user_pages_fast code Christoph Hellwig
2019-06-11 14:40 ` [PATCH 07/16] sparc64: add the missing pgd_page definition Christoph Hellwig
2019-06-11 14:40 ` [PATCH 08/16] sparc64: define untagged_addr() Christoph Hellwig
2019-06-11 19:23 ` Khalid Aziz
2019-06-11 14:40 ` [PATCH 09/16] sparc64: use the generic get_user_pages_fast code Christoph Hellwig
2019-06-11 19:35 ` Khalid Aziz
2019-06-11 14:40 ` [PATCH 10/16] mm: rename CONFIG_HAVE_GENERIC_GUP to CONFIG_HAVE_FAST_GUP Christoph Hellwig
2019-06-11 19:35 ` Khalid Aziz
2019-06-21 14:28 ` Jason Gunthorpe
2019-06-25 7:50 ` Christoph Hellwig
2019-06-11 14:40 ` [PATCH 11/16] mm: consolidate the get_user_pages* implementations Christoph Hellwig
2019-06-21 14:41 ` Jason Gunthorpe
2019-06-25 7:56 ` Christoph Hellwig
2019-06-25 11:56 ` Jason Gunthorpe
2019-06-11 14:40 ` [PATCH 12/16] mm: validate get_user_pages_fast flags Christoph Hellwig
2019-06-11 14:40 ` [PATCH 13/16] mm: move the powerpc hugepd code to mm/gup.c Christoph Hellwig
2019-06-11 14:41 ` [PATCH 14/16] mm: switch gup_hugepte to use try_get_compound_head Christoph Hellwig
2019-06-11 14:41 ` [PATCH 15/16] mm: mark the page referenced in gup_hugepte Christoph Hellwig
2019-06-11 14:41 ` [PATCH 16/16] mm: pass get_user_pages_fast iterator arguments in a structure Christoph Hellwig
2019-06-12 0:52 ` Nicholas Piggin
2019-06-12 1:09 ` Linus Torvalds
2019-06-20 12:18 ` Nicholas Piggin
2019-06-20 17:21 ` Linus Torvalds [this message]
2019-06-21 8:15 ` Christoph Hellwig
2019-06-21 23:55 ` Nicholas Piggin
2019-06-21 8:29 ` Nicholas Piggin
2019-06-12 1:27 ` Nadav Amit
2019-06-20 11:45 ` switch the remaining architectures to use generic GUP v3 Christoph Hellwig
2019-06-21 14:43 ` Jason Gunthorpe
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