Re: Time sliced CFQ io scheduler

[Andrea Arcangeli <andrea@suse.de>]

On Tue, Dec 07, 2004 at 06:25:57PM -0800, Andrew Morton wrote:
> That's a missing hint in the direct-io code.  This fixes it up:
> 
> --- 25/fs/direct-io.c~a	2004-12-07 18:12:25.491602512 -0800
> +++ 25-akpm/fs/direct-io.c	2004-12-07 18:13:13.661279608 -0800
> @@ -1161,6 +1161,8 @@ __blockdev_direct_IO(int rw, struct kioc
>  	struct dio *dio;
>  	int reader_with_isem = (rw == READ && dio_lock_type == DIO_OWN_LOCKING);
>  
> +	current->flags |= PF_SYNCWRITE;
> +
>  	if (bdev)
>  		bdev_blkbits = blksize_bits(bdev_hardsect_size(bdev));
>  
> @@ -1244,6 +1246,7 @@ __blockdev_direct_IO(int rw, struct kioc
>  out:
>  	if (reader_with_isem)
>  		up(&inode->i_sem);
> +	current->flags &= ~PF_SYNCWRITE;
>  	return retval;
>  }
>  EXPORT_SYMBOL(__blockdev_direct_IO);

that was fast ;) great, thanks!

> I don't think AS will ever meet the performance of CFQ or deadline for the

This is my expectation too, since for these apps write latency is almost
more important than read latency and writes are often sync.