Re: Re: [PATCH 2/2] raid5: For write performance, remove REQ_SYNC when write was odirect.

[majianpeng <majianpeng@gmail.com>]

On 2012-07-16 15:30 NeilBrown <neilb@suse.de> Wrote:
>On Mon, 16 Jul 2012 15:11:29 +0800 majianpeng <majianpeng@gmail.com> wrote:
>
>> On 2012-07-16 15:07 NeilBrown <neilb@suse.de> Wrote:
>> >On Mon, 16 Jul 2012 14:42:54 +0800 majianpeng <majianpeng@gmail.com> wrote:
>> >
>> >> On 2012-07-16 13:40 NeilBrown <neilb@suse.de> Wrote:
>> >> >On Mon, 16 Jul 2012 09:31:55 +0800 majianpeng <majianpeng@gmail.com> wrote:
>> >> >
>> [snip]
>> >> > Normal 'sync' requests use WRITE_SYNC which includes "REQ_NOIDLE" which means
>> >> >   /* don't anticipate more IO after this one */
>> >> > O_DIRECT request use WRITE_ODIRECT which does not include this flag.
>> >> >
>> >
>> >> Using REQ_NOIDEL to difference odirect and sync.Why not using:
>> >>  +	if (bi->bi_rw & WRITE_ODIRECT)
>> >>  +		bi->bi_rw &= ~REQ_SYNC;
>> >
>> >Because that code is wrong.  WRITE_ODIRECT is not one flag, it is two flags
>> >'or'ed together.  So this code does not do what you expect.
>> >
>> No, I used those code test and it's ok.
>> The code used & not &&.
>> Maybe I wrong?
>
>Think about it...
>
>#define REQ_WRITE               (1 << __REQ_WRITE)
>#define REQ_SYNC                (1 << __REQ_SYNC)
>
>#define RW_MASK                 REQ_WRITE
>#define WRITE                   RW_MASK
>
>#define WRITE_ODIRECT		(WRITE | REQ_SYNC)
>
>So   
>    (bi->bi_rw & WRITE_ODIRECT)
>
>will be true if either REQ_WRITE or REQ_SYNC are set in bi_rw
>So whenever REQ_SYNC is set, your code clears the flag.
>So your code is functionally identical to
>
>   bi->bi_rw &= ~REQ_SYNC;
>
>NeilBrown
>
>
Yes, thanks your time.I maked a stupid mistake.
I'll corrected by your suggestion and resend to you.