From f6762b7ad8edd6abc802542ce845d3bc8adcb92f Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Mon, 1 May 2006 20:02:05 +0200 Subject: [PATCH] pipe: enable atomic copying of pipe data to/from user space The pipe ->map() method uses kmap() to virtually map the pages, which is both slow and has known scalability issues on SMP. This patch enables atomic copying of pipe pages, by pre-faulting data and using kmap_atomic() instead. lmbench bw_pipe and lat_pipe measurements agree this is a Good Thing. Here are results from that on a UP machine with highmem (1.5GiB of RAM), running first a UP kernel, SMP kernel, and SMP kernel patched. Vanilla-UP: Pipe bandwidth: 1622.28 MB/sec Pipe bandwidth: 1610.59 MB/sec Pipe bandwidth: 1608.30 MB/sec Pipe latency: 7.3275 microseconds Pipe latency: 7.2995 microseconds Pipe latency: 7.3097 microseconds Vanilla-SMP: Pipe bandwidth: 1382.19 MB/sec Pipe bandwidth: 1317.27 MB/sec Pipe bandwidth: 1355.61 MB/sec Pipe latency: 9.6402 microseconds Pipe latency: 9.6696 microseconds Pipe latency: 9.6153 microseconds Patched-SMP: Pipe bandwidth: 1578.70 MB/sec Pipe bandwidth: 1579.95 MB/sec Pipe bandwidth: 1578.63 MB/sec Pipe latency: 9.1654 microseconds Pipe latency: 9.2266 microseconds Pipe latency: 9.1527 microseconds Signed-off-by: Jens Axboe --- fs/splice.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'fs/splice.c') diff --git a/fs/splice.c b/fs/splice.c index 0a6916423e7d..d4664a297bab 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -640,13 +640,13 @@ find_page: /* * Careful, ->map() uses KM_USER0! */ - char *src = buf->ops->map(info, buf); + char *src = buf->ops->map(info, buf, 1); char *dst = kmap_atomic(page, KM_USER1); memcpy(dst + offset, src + buf->offset, this_len); flush_dcache_page(page); kunmap_atomic(dst, KM_USER1); - buf->ops->unmap(info, buf); + buf->ops->unmap(info, buf, src); } ret = mapping->a_ops->commit_write(file, page, offset, offset+this_len); -- cgit v1.2.3