From: Dan Williams <dan.j.williams@intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tony Luck <tony.luck@intel.com>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
Peter Zijlstra <peterz@infradead.org>,
the arch/x86 maintainers <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Al Viro <viro@zeniv.linux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 0/6] use memcpy_mcsafe() for copy_to_iter()
Date: Tue, 1 May 2018 21:00:37 -0700 [thread overview]
Message-ID: <CAPcyv4idV+hp-W56gyQDN4p9SQsYz+xondgVJwQSYphUMxkYnw@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFy2LAzRbjCEghN_7SAZgAOr0RoUFDwYkkB+V91jdTg-YA@mail.gmail.com>
On Tue, May 1, 2018 at 8:33 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Tue, May 1, 2018 at 8:22 PM Dan Williams <dan.j.williams@intel.com>
> wrote:
>
>> All that to say that having a typical RAM page covering poisoned pmem
>> would complicate the 'clear badblocks' implementation.
>
> Ugh, ok.
>
> I guess the good news is that your patches aren't so big, and don't really
> affect anything else.
>
> But can we at least take this to be the impetus for just getting rid of
> that disgusting unrolled memcpy? Ablout half of the lines in the patch set
> comes from that thing.
>
> Is anybody seriously going to use pmem with some in-order chip that can't
> even get something as simple as a memory copy loop right? "git blame"
> fingers Tony Luck, I think he may have been influenced by the fumes from
> Itanium.
>
> I have some dim memory of "rep movs doesn't work well for pmem", but does
> it *seriously* need unrolling to cacheline boundaries? And if it does, who
> designed it, and why is anybody using it?
>
I think this is an FAQ from the original submission, in fact some guy
named "Linus Torvalds" asked [1]:
---
> - why does this use the complex - and slower, on modern machines -
> unrolled manual memory copy, when you might as well just use a single
>
> rep ; movsb
>
> which not only makes it smaller, but makes the exception fixup trivial.
Because current generation cpus don't give a recoverable machine
check if we consume with a "rep ; movsb" :-(
When we have that we can pick the best copy function based
on the capabilities of the cpu we are running on.
---
[1]: https://lkml.org/lkml/2016/2/18/608
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WARNING: multiple messages have this Message-ID (diff)
From: Dan Williams <dan.j.williams@intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
Tony Luck <tony.luck@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@alien8.de>,
"the arch/x86 maintainers" <x86@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andy Lutomirski <luto@amacapital.net>,
Ingo Molnar <mingo@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/6] use memcpy_mcsafe() for copy_to_iter()
Date: Tue, 1 May 2018 21:00:37 -0700 [thread overview]
Message-ID: <CAPcyv4idV+hp-W56gyQDN4p9SQsYz+xondgVJwQSYphUMxkYnw@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFy2LAzRbjCEghN_7SAZgAOr0RoUFDwYkkB+V91jdTg-YA@mail.gmail.com>
On Tue, May 1, 2018 at 8:33 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Tue, May 1, 2018 at 8:22 PM Dan Williams <dan.j.williams@intel.com>
> wrote:
>
>> All that to say that having a typical RAM page covering poisoned pmem
>> would complicate the 'clear badblocks' implementation.
>
> Ugh, ok.
>
> I guess the good news is that your patches aren't so big, and don't really
> affect anything else.
>
> But can we at least take this to be the impetus for just getting rid of
> that disgusting unrolled memcpy? Ablout half of the lines in the patch set
> comes from that thing.
>
> Is anybody seriously going to use pmem with some in-order chip that can't
> even get something as simple as a memory copy loop right? "git blame"
> fingers Tony Luck, I think he may have been influenced by the fumes from
> Itanium.
>
> I have some dim memory of "rep movs doesn't work well for pmem", but does
> it *seriously* need unrolling to cacheline boundaries? And if it does, who
> designed it, and why is anybody using it?
>
I think this is an FAQ from the original submission, in fact some guy
named "Linus Torvalds" asked [1]:
---
> - why does this use the complex - and slower, on modern machines -
> unrolled manual memory copy, when you might as well just use a single
>
> rep ; movsb
>
> which not only makes it smaller, but makes the exception fixup trivial.
Because current generation cpus don't give a recoverable machine
check if we consume with a "rep ; movsb" :-(
When we have that we can pick the best copy function based
on the capabilities of the cpu we are running on.
---
[1]: https://lkml.org/lkml/2016/2/18/608
next prev parent reply other threads:[~2018-05-02 4:00 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-01 20:45 [PATCH 0/6] use memcpy_mcsafe() for copy_to_iter() Dan Williams
2018-05-01 20:45 ` Dan Williams
2018-05-01 20:45 ` [PATCH 1/6] x86, memcpy_mcsafe: update labels in support of write fault handling Dan Williams
2018-05-01 20:45 ` Dan Williams
2018-05-01 20:45 ` [PATCH 2/6] x86, memcpy_mcsafe: return bytes remaining Dan Williams
2018-05-01 20:45 ` Dan Williams
2018-05-01 20:45 ` [PATCH 3/6] x86, memcpy_mcsafe: add write-protection-fault handling Dan Williams
2018-05-01 20:45 ` Dan Williams
2018-05-01 20:45 ` [PATCH 4/6] x86, memcpy_mcsafe: define copy_to_iter_mcsafe() Dan Williams
2018-05-01 20:45 ` Dan Williams
2018-05-01 22:17 ` kbuild test robot
2018-05-01 22:17 ` kbuild test robot
2018-05-01 22:49 ` kbuild test robot
2018-05-01 22:49 ` kbuild test robot
2018-05-01 20:45 ` [PATCH 5/6] dax: use copy_to_iter_mcsafe() in dax_iomap_actor() Dan Williams
2018-05-01 20:45 ` Dan Williams
2018-05-01 20:45 ` [PATCH 6/6] x86, nfit_test: unit test for memcpy_mcsafe() Dan Williams
2018-05-01 20:45 ` Dan Williams
2018-05-01 21:05 ` [PATCH 0/6] use memcpy_mcsafe() for copy_to_iter() Linus Torvalds
2018-05-01 21:05 ` Linus Torvalds
2018-05-01 23:02 ` Dan Williams
2018-05-01 23:02 ` Dan Williams
2018-05-01 23:28 ` Andy Lutomirski
2018-05-01 23:28 ` Andy Lutomirski
2018-05-01 23:31 ` Dan Williams
2018-05-01 23:31 ` Dan Williams
2018-05-02 0:09 ` Linus Torvalds
2018-05-02 0:09 ` Linus Torvalds
2018-05-02 2:25 ` Dan Williams
2018-05-02 2:25 ` Dan Williams
2018-05-02 2:53 ` Linus Torvalds
2018-05-02 2:53 ` Linus Torvalds
2018-05-02 3:02 ` Dan Williams
2018-05-02 3:02 ` Dan Williams
2018-05-02 3:13 ` Linus Torvalds
2018-05-02 3:13 ` Linus Torvalds
2018-05-02 3:20 ` Dan Williams
2018-05-02 3:20 ` Dan Williams
2018-05-02 3:22 ` Dan Williams
2018-05-02 3:22 ` Dan Williams
2018-05-02 3:33 ` Linus Torvalds
2018-05-02 3:33 ` Linus Torvalds
2018-05-02 4:00 ` Dan Williams [this message]
2018-05-02 4:00 ` Dan Williams
2018-05-02 4:14 ` Linus Torvalds
2018-05-02 4:14 ` Linus Torvalds
2018-05-02 5:37 ` Dan Williams
2018-05-02 5:37 ` Dan Williams
2018-05-02 16:19 ` Andy Lutomirski
2018-05-02 16:19 ` Andy Lutomirski
2018-05-02 17:47 ` Dan Williams
2018-05-02 17:47 ` Dan Williams
2018-05-02 8:30 ` Borislav Petkov
2018-05-02 8:30 ` Borislav Petkov
2018-05-02 13:52 ` Dan Williams
2018-05-02 13:52 ` Dan Williams
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