Max, did you have time to look at this? On Sat, Aug 17, 2019 at 12:21 AM Nir Soffer <nir...@gmail.com> wrote:
> When creating an image with preallocation "off" or "falloc", the first > block of the image is typically not allocated. When using Gluster > storage backed by XFS filesystem, reading this block using direct I/O > succeeds regardless of request length, fooling alignment detection. > > In this case we fallback to a safe value (4096) instead of the optimal > value (512), which may lead to unneeded data copying when aligning > requests. Allocating the first block avoids the fallback. > > When using preallocation=off, we always allocate at least one filesystem > block: > > $ ./qemu-img create -f raw test.raw 1g > Formatting 'test.raw', fmt=raw size=1073741824 > > $ ls -lhs test.raw > 4.0K -rw-r--r--. 1 nsoffer nsoffer 1.0G Aug 16 23:48 test.raw > > I did quick performance tests for these flows: > - Provisioning a VM with a new raw image. > - Copying disks with qemu-img convert to new raw target image > > I installed Fedora 29 server on raw sparse image, measuring the time > from clicking "Begin installation" until the "Reboot" button appears: > > Before(s) After(s) Diff(%) > ------------------------------- > 356 389 +8.4 > > I ran this only once, so we cannot tell much from these results. > > The second test was cloning the installation image with qemu-img > convert, doing 10 runs: > > for i in $(seq 10); do > rm -f dst.raw > sleep 10 > time ./qemu-img convert -f raw -O raw -t none -T none src.raw > dst.raw > done > > Here is a table comparing the total time spent: > > Type Before(s) After(s) Diff(%) > --------------------------------------- > real 530.028 469.123 -11.4 > user 17.204 10.768 -37.4 > sys 17.881 7.011 -60.7 > > Here we see very clear improvement in CPU usage. > > Signed-off-by: Nir Soffer <nsof...@redhat.com> > --- > block/file-posix.c | 25 +++++++++++++++++++++++++ > tests/qemu-iotests/150.out | 1 + > tests/qemu-iotests/160 | 4 ++++ > tests/qemu-iotests/175 | 19 +++++++++++++------ > tests/qemu-iotests/175.out | 8 ++++---- > tests/qemu-iotests/221.out | 12 ++++++++---- > tests/qemu-iotests/253.out | 12 ++++++++---- > 7 files changed, 63 insertions(+), 18 deletions(-) > > diff --git a/block/file-posix.c b/block/file-posix.c > index b9c33c8f6c..3964dd2021 100644 > --- a/block/file-posix.c > +++ b/block/file-posix.c > @@ -1755,6 +1755,27 @@ static int handle_aiocb_discard(void *opaque) > return ret; > } > > +/* > + * Help alignment detection by allocating the first block. > + * > + * When reading with direct I/O from unallocated area on Gluster backed > by XFS, > + * reading succeeds regardless of request length. In this case we > fallback to > + * safe aligment which is not optimal. Allocating the first block avoids > this > + * fallback. > + * > + * Returns: 0 on success, -errno on failure. > + */ > +static int allocate_first_block(int fd) > +{ > + ssize_t n; > + > + do { > + n = pwrite(fd, "\0", 1, 0); > + } while (n == -1 && errno == EINTR); > + > + return (n == -1) ? -errno : 0; > +} > + > static int handle_aiocb_truncate(void *opaque) > { > RawPosixAIOData *aiocb = opaque; > @@ -1794,6 +1815,8 @@ static int handle_aiocb_truncate(void *opaque) > /* posix_fallocate() doesn't set errno. */ > error_setg_errno(errp, -result, > "Could not preallocate new data"); > + } else if (current_length == 0) { > + allocate_first_block(fd); > } > } else { > result = 0; > @@ -1855,6 +1878,8 @@ static int handle_aiocb_truncate(void *opaque) > if (ftruncate(fd, offset) != 0) { > result = -errno; > error_setg_errno(errp, -result, "Could not resize file"); > + } else if (current_length == 0 && offset > current_length) { > + allocate_first_block(fd); > } > return result; > default: > diff --git a/tests/qemu-iotests/150.out b/tests/qemu-iotests/150.out > index 2a54e8dcfa..3cdc7727a5 100644 > --- a/tests/qemu-iotests/150.out > +++ b/tests/qemu-iotests/150.out > @@ -3,6 +3,7 @@ QA output created by 150 > === Mapping sparse conversion === > > Offset Length File > +0 0x1000 TEST_DIR/t.IMGFMT > > === Mapping non-sparse conversion === > > diff --git a/tests/qemu-iotests/160 b/tests/qemu-iotests/160 > index df89d3864b..ad2d054a47 100755 > --- a/tests/qemu-iotests/160 > +++ b/tests/qemu-iotests/160 > @@ -57,6 +57,10 @@ for skip in $TEST_SKIP_BLOCKS; do > $QEMU_IMG dd if="$TEST_IMG" of="$TEST_IMG.out" skip="$skip" -O > "$IMGFMT" \ > 2> /dev/null > TEST_IMG="$TEST_IMG.out" _check_test_img > + > + # We always write the first byte of an image. > + printf "\0" > "$TEST_IMG.out.dd" > + > dd if="$TEST_IMG" of="$TEST_IMG.out.dd" skip="$skip" status=none > > echo > diff --git a/tests/qemu-iotests/175 b/tests/qemu-iotests/175 > index 51e62c8276..c6a3a7bb1e 100755 > --- a/tests/qemu-iotests/175 > +++ b/tests/qemu-iotests/175 > @@ -37,14 +37,16 @@ trap "_cleanup; exit \$status" 0 1 2 3 15 > # the file size. This function hides the resulting difference in the > # stat -c '%b' output. > # Parameter 1: Number of blocks an empty file occupies > -# Parameter 2: Image size in bytes > +# Parameter 2: Minimal number of blocks in an image > +# Parameter 3: Image size in bytes > _filter_blocks() > { > extra_blocks=$1 > - img_size=$2 > + min_blocks=$2 > + img_size=$3 > > - sed -e "s/blocks=$extra_blocks\\(\$\\|[^0-9]\\)/nothing allocated/" \ > - -e "s/blocks=$((extra_blocks + img_size / > 512))\\(\$\\|[^0-9]\\)/everything allocated/" > + sed -e "s/blocks=$((extra_blocks + min_blocks))\\(\$\\|[^0-9]\\)/min > allocation/" \ > + -e "s/blocks=$((extra_blocks + img_size / > 512))\\(\$\\|[^0-9]\\)/max allocation/" > } > > # get standard environment, filters and checks > @@ -60,16 +62,21 @@ size=$((1 * 1024 * 1024)) > touch "$TEST_DIR/empty" > extra_blocks=$(stat -c '%b' "$TEST_DIR/empty") > > +# We always write the first byte; check how many blocks this filesystem > +# allocates to match empty image alloation. > +printf "\0" > "$TEST_DIR/empty" > +min_blocks=$(stat -c '%b' "$TEST_DIR/empty") > + > echo > echo "== creating image with default preallocation ==" > _make_test_img $size | _filter_imgfmt > -stat -c "size=%s, blocks=%b" $TEST_IMG | _filter_blocks $extra_blocks > $size > +stat -c "size=%s, blocks=%b" $TEST_IMG | _filter_blocks $extra_blocks > $min_blocks $size > > for mode in off full falloc; do > echo > echo "== creating image with preallocation $mode ==" > IMGOPTS=preallocation=$mode _make_test_img $size | _filter_imgfmt > - stat -c "size=%s, blocks=%b" $TEST_IMG | _filter_blocks $extra_blocks > $size > + stat -c "size=%s, blocks=%b" $TEST_IMG | _filter_blocks $extra_blocks > $min_blocks $size > done > > # success, all done > diff --git a/tests/qemu-iotests/175.out b/tests/qemu-iotests/175.out > index 6d9a5ed84e..263e521262 100644 > --- a/tests/qemu-iotests/175.out > +++ b/tests/qemu-iotests/175.out > @@ -2,17 +2,17 @@ QA output created by 175 > > == creating image with default preallocation == > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 > -size=1048576, nothing allocated > +size=1048576, min allocation > > == creating image with preallocation off == > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 preallocation=off > -size=1048576, nothing allocated > +size=1048576, min allocation > > == creating image with preallocation full == > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 preallocation=full > -size=1048576, everything allocated > +size=1048576, max allocation > > == creating image with preallocation falloc == > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 > preallocation=falloc > -size=1048576, everything allocated > +size=1048576, max allocation > *** done > diff --git a/tests/qemu-iotests/221.out b/tests/qemu-iotests/221.out > index 9f9dd52bb0..dca024a0c3 100644 > --- a/tests/qemu-iotests/221.out > +++ b/tests/qemu-iotests/221.out > @@ -3,14 +3,18 @@ QA output created by 221 > === Check mapping of unaligned raw image === > > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=65537 > -[{ "start": 0, "length": 66048, "depth": 0, "zero": true, "data": false, > "offset": OFFSET}] > -[{ "start": 0, "length": 66048, "depth": 0, "zero": true, "data": false, > "offset": OFFSET}] > +[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true, > "offset": OFFSET}, > +{ "start": 4096, "length": 61952, "depth": 0, "zero": true, "data": > false, "offset": OFFSET}] > +[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true, > "offset": OFFSET}, > +{ "start": 4096, "length": 61952, "depth": 0, "zero": true, "data": > false, "offset": OFFSET}] > wrote 1/1 bytes at offset 65536 > 1 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) > -[{ "start": 0, "length": 65536, "depth": 0, "zero": true, "data": false, > "offset": OFFSET}, > +[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true, > "offset": OFFSET}, > +{ "start": 4096, "length": 61440, "depth": 0, "zero": true, "data": > false, "offset": OFFSET}, > { "start": 65536, "length": 1, "depth": 0, "zero": false, "data": true, > "offset": OFFSET}, > { "start": 65537, "length": 511, "depth": 0, "zero": true, "data": false, > "offset": OFFSET}] > -[{ "start": 0, "length": 65536, "depth": 0, "zero": true, "data": false, > "offset": OFFSET}, > +[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true, > "offset": OFFSET}, > +{ "start": 4096, "length": 61440, "depth": 0, "zero": true, "data": > false, "offset": OFFSET}, > { "start": 65536, "length": 1, "depth": 0, "zero": false, "data": true, > "offset": OFFSET}, > { "start": 65537, "length": 511, "depth": 0, "zero": true, "data": false, > "offset": OFFSET}] > *** done > diff --git a/tests/qemu-iotests/253.out b/tests/qemu-iotests/253.out > index 607c0baa0b..3d08b305d7 100644 > --- a/tests/qemu-iotests/253.out > +++ b/tests/qemu-iotests/253.out > @@ -3,12 +3,16 @@ QA output created by 253 > === Check mapping of unaligned raw image === > > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048575 > -[{ "start": 0, "length": 1048576, "depth": 0, "zero": true, "data": > false, "offset": OFFSET}] > -[{ "start": 0, "length": 1048576, "depth": 0, "zero": true, "data": > false, "offset": OFFSET}] > +[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true, > "offset": OFFSET}, > +{ "start": 4096, "length": 1044480, "depth": 0, "zero": true, "data": > false, "offset": OFFSET}] > +[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true, > "offset": OFFSET}, > +{ "start": 4096, "length": 1044480, "depth": 0, "zero": true, "data": > false, "offset": OFFSET}] > wrote 65535/65535 bytes at offset 983040 > 63.999 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) > -[{ "start": 0, "length": 983040, "depth": 0, "zero": true, "data": false, > "offset": OFFSET}, > +[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true, > "offset": OFFSET}, > +{ "start": 4096, "length": 978944, "depth": 0, "zero": true, "data": > false, "offset": OFFSET}, > { "start": 983040, "length": 65536, "depth": 0, "zero": false, "data": > true, "offset": OFFSET}] > -[{ "start": 0, "length": 983040, "depth": 0, "zero": true, "data": false, > "offset": OFFSET}, > +[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true, > "offset": OFFSET}, > +{ "start": 4096, "length": 978944, "depth": 0, "zero": true, "data": > false, "offset": OFFSET}, > { "start": 983040, "length": 65536, "depth": 0, "zero": false, "data": > true, "offset": OFFSET}] > *** done > -- > 2.20.1 > >