Messages in this thread | | | From | Sven Van Asbroeck <> | Date | Thu, 9 Jul 2020 08:16:30 -0400 | Subject | Re: [PATCH v1 2/2] romfs: address performance regression since v3.10 |
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Hello Al,
You are the closest I could find to a romfs maintainer. get_maintainer.pl doesn't appear to list any.
This attempted performance regression fix didn't generate much feedback (to say the least). It's however a real issue for us when supporting a legacy product where we don't have the luxury of switching to a better-supported fs.
Is there anything I can do to further this? Is lkml currently accepting bug / regression fixes to romfs, or is it obsolete?
Many thanks, Sven
On Mon, Jun 22, 2020 at 8:45 PM Sven Van Asbroeck <thesven73@gmail.com> wrote: > > Problem > ------- > romfs sequential read performance has regressed very badly since > v3.10. Currently, reading a large file inside a romfs image is > up to 12x slower compared to reading the romfs image directly. > > Benchmarks: > - use a romfs image which contains a single 250M file > - calculate the md5sum of the romfs image directly (test 1) > $ time md5sum image.romfs > - loop-mount the romfs image, and calc the md5sum of the file > inside it (test 2) > $ mount -o loop,ro image.romfs /mnt/romfs > $ time md5sum /mnt/romfs/file > - drop caches in between > $ echo 3 > /proc/sys/vm/drop_caches > > imx6 (arm cortex a9) on emmc, running v5.7.2: > (test 1) 5 seconds > (test 2) 60 seconds (12x slower) > > Intel i7-3630QM on Samsung SSD 850 EVO (EMT02B6Q), > running Ubuntu with v4.15.0-106-generic: > (test 1) 1.3 seconds > (test 2) 3.3 seconds (2.5x slower) > > To show that a regression has occurred since v3.10: > > imx6 on emmc, running v3.10.17: > (test 1) 16 seconds > (test 2) 18 seconds > > Proposed Solution > ----------------- > Increase the blocksize from 1K to PAGE_SIZE. This brings the > sequential read performance close to where it was on v3.10: > > imx6 on emmc, running v5.7.2: > (test 2 1K blocksize) 60 seconds > (test 2 4K blocksize) 22 seconds > > Intel on Ubuntu running v4.15: > (test 2 1K blocksize) 3.3 seconds > (test 2 4K blocksize) 1.9 seconds > > There is a risk that this may increase latency on random- > access workloads. But the test below suggests that this > is not a concern: > > Benchmark: > - use a 630M romfs image consisting of 9600 files > - loop-mount the romfs image > $ mount -o loop,ro image.romfs /mnt/romfs > - drop all caches > - list all files in the filesystem (test 3) > $ time find /mnt/romfs > /dev/null > > imx6 on emmc, running v5.7.2: > (test 3 1K blocksize) 9.5 seconds > (test 3 4K blocksize) 9 seconds > > Intel on Ubuntu, running v4.15: > (test 3 1K blocksize) 1.4 seconds > (test 3 4K blocksize) 1.2 seconds > > Practical Solution > ------------------ > Introduce a mount-option called 'largeblocks'. If present, > increase the blocksize for much better sequential performance. > > Note that the Linux block layer can only support n-K blocks if > the underlying block device length is also aligned to n-K. This > may not always be the case. Therefore, the driver will pick the > largest blocksize which the underlying block device can support. > > Cc: Al Viro <viro@zeniv.linux.org.uk> > Cc: Deepa Dinamani <deepa.kernel@gmail.com> > Cc: David Howells <dhowells@redhat.com> > Cc: "Darrick J. Wong" <darrick.wong@oracle.com> > Cc: Janos Farkas <chexum+dev@gmail.com> > Cc: Jeff Layton <jlayton@kernel.org> > To: linux-kernel@vger.kernel.org > Signed-off-by: Sven Van Asbroeck <TheSven73@gmail.com> > --- > fs/romfs/super.c | 62 ++++++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 57 insertions(+), 5 deletions(-) > > diff --git a/fs/romfs/super.c b/fs/romfs/super.c > index 6fecdea791f1..93565aeaa43c 100644 > --- a/fs/romfs/super.c > +++ b/fs/romfs/super.c > @@ -65,7 +65,7 @@ > #include <linux/slab.h> > #include <linux/init.h> > #include <linux/blkdev.h> > -#include <linux/fs_context.h> > +#include <linux/fs_parser.h> > #include <linux/mount.h> > #include <linux/namei.h> > #include <linux/statfs.h> > @@ -460,6 +460,54 @@ static __u32 romfs_checksum(const void *data, int size) > return sum; > } > > +enum romfs_param { > + Opt_largeblocks, > +}; > + > +static const struct fs_parameter_spec romfs_fs_parameters[] = { > + fsparam_flag("largeblocks", Opt_largeblocks), > + {} > +}; > + > +/* > + * Parse a single mount parameter. > + */ > +static int romfs_parse_param(struct fs_context *fc, struct fs_parameter *param) > +{ > + struct fs_parse_result result; > + int opt; > + > + opt = fs_parse(fc, romfs_fs_parameters, param, &result); > + if (opt < 0) > + return opt; > + > + switch (opt) { > + case Opt_largeblocks: > + fc->fs_private = (void *) 1; > + break; > + default: > + return -EINVAL; > + } > + > + return 0; > +} > + > +/* > + * pick the largest blocksize which the underlying block device > + * is a multiple of. Or fall back to legacy (ROMBSIZE). > + */ > +static int romfs_largest_blocksize(struct super_block *sb) > +{ > + loff_t device_sz = i_size_read(sb->s_bdev->bd_inode); > + int blksz; > + > + for (blksz = PAGE_SIZE; blksz > ROMBSIZE; blksz >>= 1) > + if ((device_sz % blksz) == 0) > + break; > + > + return blksz; > +} > + > /* > * fill in the superblock > */ > @@ -467,17 +515,19 @@ static int romfs_fill_super(struct super_block *sb, struct fs_context *fc) > { > struct romfs_super_block *rsb; > struct inode *root; > - unsigned long pos, img_size; > + unsigned long pos, img_size, dev_blocksize; > const char *storage; > size_t len; > int ret; > > #ifdef CONFIG_BLOCK > + dev_blocksize = fc->fs_private ? romfs_largest_blocksize(sb) : > + ROMBSIZE; > if (!sb->s_mtd) { > - sb_set_blocksize(sb, ROMBSIZE); > + sb_set_blocksize(sb, dev_blocksize); > } else { > - sb->s_blocksize = ROMBSIZE; > - sb->s_blocksize_bits = blksize_bits(ROMBSIZE); > + sb->s_blocksize = dev_blocksize; > + sb->s_blocksize_bits = blksize_bits(dev_blocksize); > } > #endif > > @@ -573,6 +623,7 @@ static int romfs_get_tree(struct fs_context *fc) > static const struct fs_context_operations romfs_context_ops = { > .get_tree = romfs_get_tree, > .reconfigure = romfs_reconfigure, > + .parse_param = romfs_parse_param, > }; > > /* > @@ -607,6 +658,7 @@ static struct file_system_type romfs_fs_type = { > .owner = THIS_MODULE, > .name = "romfs", > .init_fs_context = romfs_init_fs_context, > + .parameters = romfs_fs_parameters, > .kill_sb = romfs_kill_sb, > .fs_flags = FS_REQUIRES_DEV, > }; > -- > 2.17.1 >
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