Direct io on block device has performance regression on 2.6.x kernel - fix AIO path

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To: <linux-kernel@vger.kernel.org>
Date:	Tue, 8 Mar 2005 17:49:16 -0800

This patch adds block device direct I/O for AIO path.

30% performance gain!!

                        AIO (io_submit)
2.6.9 206,917
2.6.9+patches 268,484

- Ken

Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>

--- linux-2.6.9/drivers/char/raw.c 2005-03-08 17:22:07.000000000 -0800
+++ linux-2.6.9.ken/drivers/char/raw.c 2005-03-08 17:25:38.000000000 -0800
@@ -385,21 +385,148 @@ static ssize_t raw_file_write(struct fil
         return raw_file_rw(file, (char __user *) buf, count, ppos, WRITE);
 }

-static ssize_t raw_file_aio_write(struct kiocb *iocb, const char __user *buf,
- size_t count, loff_t pos)
+int raw_end_aio(struct bio *bio, unsigned int bytes_done, int error)
 {
- struct iovec local_iov = {
- .iov_base = (char __user *)buf,
- .iov_len = count
- };
+ struct kiocb* iocb = bio->bi_private;
+ atomic_t* bio_count = (atomic_t*) &iocb->private;
+
+ if ((bio->bi_rw & 0x1) == READ)
+ bio_check_pages_dirty(bio);
+ else {
+ int i;
+ struct bio_vec *bvec = bio->bi_io_vec;
+ struct page *page;
+ for (i = 0; i < bio->bi_vcnt; i++) {
+ page = bvec[i].bv_page;
+ if (page)
+ put_page(page);
+ }
+ bio_put(bio);
+ }
+ if (atomic_dec_and_test(bio_count))
+ aio_complete(iocb, iocb->ki_nbytes, 0);

- return generic_file_aio_write_nolock(iocb, &local_iov, 1, &iocb->ki_pos);
+ return 0;
 }

+static ssize_t raw_file_aio_rw(struct kiocb *iocb, char __user *buf,
+ size_t count, loff_t pos, int rw)
+{
+ struct inode * inode = iocb->ki_filp->f_mapping->host;
+ unsigned long blkbits = inode->i_blkbits;
+ unsigned long blocksize_mask = (1<< blkbits) - 1;
+ struct page * quick_list[PAGE_QUICK_LIST];
+ int nr_pages, cur_offset, cur_len;
+ struct bio * bio;
+ unsigned long ret;
+ unsigned long addr = (unsigned long) buf;
+ loff_t size;
+ int pg_idx;
+ atomic_t *bio_count = (atomic_t *) &iocb->private;
+
+ if (count == 0)
+ return 0;
+
+ /* first check the alignment */
+ if (addr & blocksize_mask || count & blocksize_mask ||
+ count < 0 || pos & blocksize_mask)
+ return -EINVAL;
+
+ size = i_size_read(inode);
+ if (pos >= size)
+ return -ENXIO;
+ if (pos + count > size)
+ count = size - pos;
+
+ nr_pages = (addr + count + PAGE_SIZE - 1) / PAGE_SIZE -
+ addr / PAGE_SIZE;
+
+ pg_idx = PAGE_QUICK_LIST;
+ atomic_set(bio_count, 1);
+
+start:
+ bio = bio_alloc(GFP_KERNEL, nr_pages);
+ if (unlikely(bio == NULL)) {
+ if (atomic_read(bio_count) == 1)
+ return -ENOMEM;
+ else {
+ iocb->ki_nbytes = addr - (unsigned long) buf;
+ goto out;
+ }
+ }
+
+ /* initialize bio */
+ bio->bi_bdev = I_BDEV(inode);
+ bio->bi_end_io = raw_end_aio;
+ bio->bi_private = iocb;
+ bio->bi_sector = pos >> blkbits;
+
+ while (count > 0) {
+ cur_offset = addr & ~PAGE_MASK;
+ cur_len = PAGE_SIZE - cur_offset;
+ if (cur_len > count)
+ cur_len = count;
+
+ if (pg_idx >= PAGE_QUICK_LIST) {
+ down_read(&current->mm->mmap_sem);
+ ret = get_user_pages(current, current->mm, addr,
+ min(nr_pages, PAGE_QUICK_LIST),
+ rw==READ, 0, quick_list, NULL);
+ up_read(&current->mm->mmap_sem);
+ if (unlikely(ret < 0)) {
+ bio_put(bio);
+ if (atomic_read(bio_count) == 1)
+ return ret;
+ else {
+ iocb->ki_nbytes = addr - (unsigned long) buf;
+ goto out;
+ }
+ }
+ pg_idx = 0;
+ }
+
+ if (unlikely(!bio_add_page(bio, quick_list[pg_idx], cur_len, cur_offset))) {
+ atomic_inc(bio_count);
+ if (rw == READ)
+ bio_set_pages_dirty(bio);
+ submit_bio(rw, bio);
+ pos += addr - (unsigned long) buf;
+ goto start;
+ }
+
+ addr += cur_len;
+ count -= cur_len;
+ pg_idx++;
+ nr_pages--;
+ }
+
+ atomic_inc(bio_count);
+ if (rw == READ)
+ bio_set_pages_dirty(bio);
+ submit_bio(rw, bio);
+out:
+ blk_run_address_space(inode->i_mapping);
+ if (atomic_dec_and_test(bio_count)) {
+ aio_complete(iocb, iocb->ki_nbytes, 0);
+ }
+
+ return -EIOCBQUEUED;
+}
+
+ssize_t raw_file_aio_read(struct kiocb *iocb, char __user *buf, size_t count, loff_t pos)
+{
+ return raw_file_aio_rw(iocb, buf, count, pos, READ);
+}
+
+static ssize_t raw_file_aio_write(struct kiocb *iocb, const char __user *buf,
+ size_t count, loff_t pos)
+{
+ return raw_file_aio_rw(iocb, (char __user *) buf, count, pos, WRITE);
+}

 static struct file_operations raw_fops = {
         .read = raw_file_read,
- .aio_read = generic_file_aio_read,
+ .aio_read = raw_file_aio_read,
         .write = raw_file_write,
         .aio_write = raw_file_aio_write,
         .open = raw_open,

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• Previous message: Robert Han***: "Re: select(2), usbserial, tty's and disconnect"
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