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From: Balbir Singh <bsingharora@gmail.com>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: "Luck, Tony" <tony.luck@intel.com>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Matthew Wilcox <mawilcox@microsoft.com>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [RESEND 2/3] powerpc/memcpy: Add memcpy_mcsafe for pmem
Date: Fri, 6 Apr 2018 19:25:52 +1000	[thread overview]
Message-ID: <CAKTCnz=LD_uO7bdwFHDHy9KHHJ_dPA1LdxF1Pm7OUFFGr4s_VA@mail.gmail.com> (raw)
In-Reply-To: <20180406112600.454432f0@roar.ozlabs.ibm.com>

On Fri, Apr 6, 2018 at 11:26 AM, Nicholas Piggin <npiggin@gmail.com> wrote:
> On Thu, 05 Apr 2018 16:40:26 -0400
> Jeff Moyer <jmoyer@redhat.com> wrote:
>
>> Nicholas Piggin <npiggin@gmail.com> writes:
>>
>> > On Thu, 5 Apr 2018 15:53:07 +1000
>> > Balbir Singh <bsingharora@gmail.com> wrote:
>> >> I'm thinking about it, I wonder what "bytes remaining" mean in pmem context
>> >> in the context of a machine check exception. Also, do we want to be byte
>> >> accurate or cache-line accurate for the bytes remaining? The former is much
>> >> easier than the latter :)
>> >
>> > The ideal would be a linear measure of how much of your copy reached
>> > (or can reach) non-volatile storage with nothing further copied. You
>> > may have to allow for some relaxing of the semantics depending on
>> > what the architecture can support.
>>
>> I think you've got that backwards.  memcpy_mcsafe is used to copy *from*
>> persistent memory.  The idea is to catch errors when reading pmem, not
>> writing to it.
>>

I know the comment in x86 says posted writes and cares for only loads, but I
don't see why both sides should not be handled.

>> > What's the problem with just counting bytes copied like usercopy --
>> > why is that harder than cacheline accuracy?
>>
>> He said the former (i.e. bytes) is easier.  So, I think you're on the
>> same page.  :)
>
> Oh well that makes a lot more sense in my mind now, thanks :)

I thought the cache-aligned might make sense, since usually we'd expect the
failure to be at a cache-line level, but our copy_tofrom_user does accurate
accounting

Balbir Singh.
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Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm

WARNING: multiple messages have this Message-ID (diff)
From: Balbir Singh <bsingharora@gmail.com>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: Jeff Moyer <jmoyer@redhat.com>,
	"Luck, Tony" <tony.luck@intel.com>,
	Matthew Wilcox <mawilcox@microsoft.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [RESEND 2/3] powerpc/memcpy: Add memcpy_mcsafe for pmem
Date: Fri, 6 Apr 2018 19:25:52 +1000	[thread overview]
Message-ID: <CAKTCnz=LD_uO7bdwFHDHy9KHHJ_dPA1LdxF1Pm7OUFFGr4s_VA@mail.gmail.com> (raw)
In-Reply-To: <20180406112600.454432f0@roar.ozlabs.ibm.com>

On Fri, Apr 6, 2018 at 11:26 AM, Nicholas Piggin <npiggin@gmail.com> wrote:
> On Thu, 05 Apr 2018 16:40:26 -0400
> Jeff Moyer <jmoyer@redhat.com> wrote:
>
>> Nicholas Piggin <npiggin@gmail.com> writes:
>>
>> > On Thu, 5 Apr 2018 15:53:07 +1000
>> > Balbir Singh <bsingharora@gmail.com> wrote:
>> >> I'm thinking about it, I wonder what "bytes remaining" mean in pmem context
>> >> in the context of a machine check exception. Also, do we want to be byte
>> >> accurate or cache-line accurate for the bytes remaining? The former is much
>> >> easier than the latter :)
>> >
>> > The ideal would be a linear measure of how much of your copy reached
>> > (or can reach) non-volatile storage with nothing further copied. You
>> > may have to allow for some relaxing of the semantics depending on
>> > what the architecture can support.
>>
>> I think you've got that backwards.  memcpy_mcsafe is used to copy *from*
>> persistent memory.  The idea is to catch errors when reading pmem, not
>> writing to it.
>>

I know the comment in x86 says posted writes and cares for only loads, but I
don't see why both sides should not be handled.

>> > What's the problem with just counting bytes copied like usercopy --
>> > why is that harder than cacheline accuracy?
>>
>> He said the former (i.e. bytes) is easier.  So, I think you're on the
>> same page.  :)
>
> Oh well that makes a lot more sense in my mind now, thanks :)

I thought the cache-aligned might make sense, since usually we'd expect the
failure to be at a cache-line level, but our copy_tofrom_user does accurate
accounting

Balbir Singh.

  reply	other threads:[~2018-04-06  9:25 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-04 23:19 [RESEND 0/3] Add support for memcpy_mcsafe Balbir Singh
2018-04-04 23:19 ` Balbir Singh
2018-04-04 23:19 ` [RESEND 1/3] powerpc/mce: Bug fixes for MCE handling in kernel space Balbir Singh
2018-04-04 23:19   ` Balbir Singh
2018-04-04 23:49   ` Nicholas Piggin
2018-04-04 23:49     ` Nicholas Piggin
2018-04-05  1:11     ` Balbir Singh
2018-04-05  1:11       ` Balbir Singh
2018-04-04 23:19 ` [RESEND 2/3] powerpc/memcpy: Add memcpy_mcsafe for pmem Balbir Singh
2018-04-04 23:19   ` Balbir Singh
2018-04-04 23:57   ` Nicholas Piggin
2018-04-04 23:57     ` Nicholas Piggin
2018-04-05  3:00     ` Dan Williams
2018-04-05  3:00       ` Dan Williams
2018-04-05  5:04       ` Nicholas Piggin
2018-04-05  5:04         ` Nicholas Piggin
2018-04-05  5:53         ` Balbir Singh
2018-04-05  5:53           ` Balbir Singh
2018-04-05  6:45           ` Nicholas Piggin
2018-04-05  6:45             ` Nicholas Piggin
2018-04-05 15:00             ` Dan Williams
2018-04-05 15:00               ` Dan Williams
2018-05-01 20:57               ` Dan Williams
2018-05-01 20:57                 ` Dan Williams
2018-05-02 12:36                 ` Balbir Singh
2018-05-02 12:36                   ` Balbir Singh
2018-04-05 20:40             ` Jeff Moyer
2018-04-05 20:40               ` Jeff Moyer
2018-04-06  1:26               ` Nicholas Piggin
2018-04-06  1:26                 ` Nicholas Piggin
2018-04-06  9:25                 ` Balbir Singh [this message]
2018-04-06  9:25                   ` Balbir Singh
2018-04-06 15:46                   ` Luck, Tony
2018-04-06 15:46                     ` Luck, Tony
2018-04-04 23:19 ` [RESEND 3/3] powerpc/mce: Handle memcpy_mcsafe Balbir Singh
2018-04-04 23:19   ` Balbir Singh

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