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Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback supp
From: |
Jeff Moyer |
Subject: |
Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support |
Date: |
Thu, 18 Apr 2019 12:10:44 -0400 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) |
Dan Williams <address@hidden> writes:
> On Fri, Apr 12, 2019 at 6:12 AM Jeff Moyer <address@hidden> wrote:
>>
>> Jan Kara <address@hidden> writes:
>>
>> > On Thu 11-04-19 07:51:48, Dan Williams wrote:
>> >> On Tue, Apr 9, 2019 at 9:09 PM Pankaj Gupta <address@hidden> wrote:
>> >> > + } else {
>> >> > + if (nd_region->flush(nd_region))
>> >> > + rc = -EIO;
>> >>
>> >> Given the common case wants to be fast and synchronous I think we
>> >> should try to avoid retpoline overhead by default. So something like
>> >> this:
>> >>
>> >> if (nd_region->flush == generic_nvdimm_flush)
>> >> rc = generic_nvdimm_flush(...);
>> >
>> > I'd either add a comment about avoiding retpoline overhead here or just
>> > make ->flush == NULL mean generic_nvdimm_flush(). Just so that people don't
>> > get confused by the code.
>>
>> Isn't this premature optimization? I really don't like adding things
>> like this without some numbers to show it's worth it.
>
> I don't think it's premature given this optimization technique is
> already being deployed elsewhere, see:
>
> https://lwn.net/Articles/774347/
The technique is fine, but that doesn't mean it should be applied
everywhere. Is *this* code path really going to benefit from the
optimization?
-Jeff
- [Qemu-devel] [PATCH v5 0/6] virtio pmem driver, Pankaj Gupta, 2019/04/10
- [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support, Pankaj Gupta, 2019/04/10
- Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support, Jan Kara, 2019/04/12
- Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support, Jeff Moyer, 2019/04/12
- Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support, Pankaj Gupta, 2019/04/18
- Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support, Dan Williams, 2019/04/18
- Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support,
Jeff Moyer <=
- Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support, Christoph Hellwig, 2019/04/18
- Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support, Dan Williams, 2019/04/18
- Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support, Jeff Moyer, 2019/04/22
- Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support, Dan Williams, 2019/04/22
- Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support, Jeff Moyer, 2019/04/22
- Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support, Pankaj Gupta, 2019/04/23
[Qemu-devel] [PATCH v5 4/6] dax: check synchronous mapping is supported, Pankaj Gupta, 2019/04/10
[Qemu-devel] [PATCH v5 2/5] virtio-pmem: Add virtio pmem driver, Pankaj Gupta, 2019/04/10