linux-kernel - Re: [PATCH v2 3/3] x86: remove unneeded flush in arch_copy_from_iter

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Date:   Wed, 26 Oct 2016 22:57:04 +0300
From:   Boaz Harrosh <boaz@...xistor.com>
To:     Brian Boylston <brian.boylston@....com>, linux-nvdimm@...ts.01.org
CC:     oliver.moreno@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 3/3] x86: remove unneeded flush in arch_copy_from_iter_pmem()

On 10/26/2016 06:50 PM, Brian Boylston wrote:
> copy_from_iter_nocache() now uses nocache copies for all types of iovecs
> on x86, so the flush in arch_copy_from_iter_pmem() is no longer needed.
> 
> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: <x86@...nel.org>
> Cc: Al Viro <viro@...IV.linux.org.uk>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Brian Boylston <brian.boylston@....com>
> Reviewed-by: Toshi Kani <toshi.kani@....com>
> Reported-by: Oliver Moreno <oliver.moreno@....com>
> ---
>  arch/x86/include/asm/pmem.h | 19 +------------------
>  1 file changed, 1 insertion(+), 18 deletions(-)
> 
> diff --git a/arch/x86/include/asm/pmem.h b/arch/x86/include/asm/pmem.h
> index 643eba4..2fbf4ae 100644
> --- a/arch/x86/include/asm/pmem.h
> +++ b/arch/x86/include/asm/pmem.h
> @@ -72,15 +72,6 @@ static inline void arch_wb_cache_pmem(void *addr, size_t size)
>  		clwb(p);
>  }
>  
> -/*
> - * copy_from_iter_nocache() on x86 only uses non-temporal stores for iovec
> - * iterators, so for other types (bvec & kvec) we must do a cache write-back.
> - */
> -static inline bool __iter_needs_pmem_wb(struct iov_iter *i)
> -{
> -	return iter_is_iovec(i) == false;
> -}
> -
>  /**
>   * arch_copy_from_iter_pmem - copy data from an iterator to PMEM
>   * @addr:	PMEM destination address
> @@ -92,15 +83,7 @@ static inline bool __iter_needs_pmem_wb(struct iov_iter *i)
>  static inline size_t arch_copy_from_iter_pmem(void *addr, size_t bytes,
>  		struct iov_iter *i)
>  {
> -	size_t len;
> -
> -	/* TODO: skip the write-back by always using non-temporal stores */
> -	len = copy_from_iter_nocache(addr, bytes, i);
> -
> -	if (__iter_needs_pmem_wb(i))
> -		arch_wb_cache_pmem(addr, bytes);
> -
> -	return len;
> +	return copy_from_iter_nocache(addr, bytes, i);

I wish you would remove all this completely. Don't see the point for it anymore 

Thanks a lot for doing this. I have this patch for ages in my trees and was too
lasy to fight them through. Yes it is a big boost for many workloads.

Lots of gratitude
Boaz

>  }
>  
>  /**
>