Messages in this thread | | | Date | Tue, 1 Jul 2003 08:48:15 +0530 | From | Suparna Bhattacharya <> | Subject | Re: [PATCH 2.5.73-mm2] aio O_DIRECT no readahead |
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On Mon, Jun 30, 2003 at 06:19:51PM -0700, Daniel McNeil wrote: > More testing on AIO with O_DIRECT and /dev/raw/. Doing AIO reads was > using a lot more cpu time than using dd on the raw partition even with > the io_queue_wait patch. Found out that aio is doing readahead even > for O_DIRECT. Here's a patch that fixes it. Here are some output
That was a good catch. Thanks !
> from time on reading a 90mb partition on a raw device with 32k i/o: > > CMD Kernel I/O real user sys > RUN version size > === ====== === ==== ==== === > dd 2.5.73-mm2: 32k 2.514s 0.000s 0.200s > aio (1 iocb) 2.5.73-mm2: 32k 3.408s 1.120s 2.250s > aio (32 iocb) 2.5.73-mm2: 32k 2.994s 0.830s 2.160s > aio (1 iocb) 2.5.73-mm2+patch.aiodio 32k 2.509s 0.850s 1.660s > aio (1 iocb) 2.5.73-mm2+patch.aiodio > +patch.io_queue_wait 32k 2.566s 0.010s 0.240s > aio (32 iocb) 2.5.73-mm2+patch.aiodio > +patch.io_queue_wait 32k 2.465s 0.010s 0.080s > > With this patch and my previous io_queue_wait patch the cpu time > drops down to very little when doing AIO with O_DIRECT. > > Daniel McNeil <daniel@osdl.org>
> --- linux-2.5.73-mm2/fs/aio.c 2003-06-30 16:39:15.874216228 -0700 > +++ linux-2.5.73-mm2.aiodio/fs/aio.c 2003-06-30 15:38:46.000000000 -0700 > @@ -1380,15 +1380,20 @@ ssize_t aio_setup_iocb(struct kiocb *kio > break; > ret = -EINVAL; > if (file->f_op->aio_read) { > - struct address_space *mapping = > - file->f_dentry->d_inode->i_mapping; > - unsigned long index = kiocb->ki_pos >> PAGE_CACHE_SHIFT; > - unsigned long end = (kiocb->ki_pos + kiocb->ki_left) > - >> PAGE_CACHE_SHIFT; > - > - for (; index < end; index++) { > - page_cache_readahead(mapping, &file->f_ra, > - file, index); > + /* > + * Do not do readahead for DIRECT i/o > + */ > + if (!(file->f_flags & O_DIRECT)) { > + struct address_space *mapping = > + file->f_dentry->d_inode->i_mapping; > + unsigned long index = kiocb->ki_pos >> PAGE_CACHE_SHIFT; > + unsigned long end = (kiocb->ki_pos + kiocb->ki_left) > + >> PAGE_CACHE_SHIFT; > + > + for (; index < end; index++) { > + page_cache_readahead(mapping, &file->f_ra, > + file, index); > + } > } > kiocb->ki_retry = aio_pread; > }
-- Suparna Bhattacharya (suparna@in.ibm.com) Linux Technology Center IBM Software Labs, India
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