Messages in this thread Patch in this message | | | Subject | [PATCH 2.5.73-mm2] aio O_DIRECT no readahead | From | Daniel McNeil <> | Date | 30 Jun 2003 18:19:51 -0700 |
| |
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 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; } | |