On 4/3/11 11:07 AM, Zeev Tarantov wrote:
> While testing zram I ran a script that creates a block devices,
> creates a filesystem on in and untars Qt on that filesystem.
> I was surprised to find ext4_mb_scan_aligned near the top of the profile output.
> This was evidently because the command "mke2fs -t ext4 -m 0 -I 128 -O
> ^has_journal,^ext_attr <block device>"
> created a filesystem with (output of tune2fs):
> RAID stride: 1
> RAID stripe width: 1
mke2fs queries the block device for its geometry, based on what is
reported via sysfs:
/*
* Sets the geometry of a device (stripe/stride), and returns the
* device's alignment offset, if any, or a negative error.
*/
static int get_device_geometry( ...
...
min_io = blkid_topology_get_minimum_io_size(tp);
opt_io = blkid_topology_get_optimal_io_size(tp);
...
fs_param->s_raid_stride = min_io / blocksize;
fs_param->s_raid_stripe_width = opt_io / blocksize;
What does
# blockdev --getiomin --getioopt /dev/<yourdevice>
say for your device?
The device may be reporting odd values, but mke2fs probably
should be smart enough not to set block-sized stripe unit and width...
-Eric
> I thought this strange and removed these values using debugfs:
> set_super_value raid_stride 0
> set_super_value raid_stripe_width 0
>
> With this "fix" the symbol ext4_mb_scan_aligned disappeared from perf's output:
>
> 18.98% -3.66% gzip [.] zip
> 0.00% +14.84% [kernel.kallsyms] [k] ext4_mb_scan_aligned
> 17.91% -3.44% gzip [.]
> treat_file.part.4.2264
> 13.73% -2.47% [csnappy_compress] [k]
> snappy_compress_fragment
> 3.96% -0.77% [kernel.kallsyms] [k]
> copy_user_generic_string
> 3.05% -0.41% libc-2.13.so [.] __memcpy_ssse3
> 0.89% +1.49% [kernel.kallsyms] [k] _raw_spin_lock
> 2.63% -0.49% [kernel.kallsyms] [k] __memcpy
> 1.61% -0.17% [kernel.kallsyms] [k] __memset
> 0.78% -0.11% [kernel.kallsyms] [k] ext4_mark_iloc_dirty
> 0.63% -0.11% [kernel.kallsyms] [k] system_call
> 0.66% -0.14% gzip [.] treat_stdin.2262
> 0.58% -0.12% libc-2.13.so [.] _int_malloc
>
> This is using mke2fs 1.41.14 (22-Dec-2010) on Linux 2.6.38.2.
>
> Is this expected behavior? Do you need me to provide more information?
>
> regards,
> -Z.T.
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