Re: [RFC] what to do with IOCB_DSYNC?

[Ingo Molnar <mingo@kernel.org>]

* Ingo Molnar <mingo@kernel.org> wrote:

> 
> * Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> 
> > On Mon, May 23, 2022 at 10:03:45AM -0600, Jens Axboe wrote:
> > > clear_user()
> > > 32	~96MB/sec
> > > 64	195MB/sec
> > > 128	386MB/sec
> > > 1k	2.7GB/sec
> > > 4k	7.8GB/sec
> > > 16k	14.8GB/sec
> > > 
> > > copy_from_zero_page()
> > > 32	~96MB/sec
> > > 64	193MB/sec
> > > 128	383MB/sec
> > > 1k	2.9GB/sec
> > > 4k	9.8GB/sec
> > > 16k	21.8GB/sec
> > 
> > Just FYI, on x86, Samuel Neves proposed some nice clear_user()
> > performance improvements that were forgotten about:
> > 
> > https://lore.kernel.org/lkml/20210523180423.108087-1-sneves@dei.uc.pt/
> > https://lore.kernel.org/lkml/Yk9yBcj78mpXOOLL@zx2c4.com/
> > 
> > Hoping somebody picks this up at some point...
> 
> Those ~2x speedup numbers are indeed looking very nice:
> 
> | After this patch, on a Skylake CPU, these are the
> | before/after figures:
> |
> | $ dd if=/dev/zero of=/dev/null bs=1024k status=progress
> | 94402248704 bytes (94 GB, 88 GiB) copied, 6 s, 15.7 GB/s
> |
> | $ dd if=/dev/zero of=/dev/null bs=1024k status=progress
> | 446476320768 bytes (446 GB, 416 GiB) copied, 15 s, 29.8 GB/s
> 
> Patch fell through the cracks & it doesn't apply anymore:
> 
>   checking file arch/x86/lib/usercopy_64.c
>   Hunk #2 FAILED at 17.
>   1 out of 2 hunks FAILED
> 
> Would be nice to re-send it.

Turns out Boris just sent a competing optimization to clear_user() 3 days ago:

  https://lore.kernel.org/r/YozQZMyQ0NDdD8cH@zn.tnic

Thanks,

	Ingo