On Tue, Jan 25, 2011 at 11:35 AM, Shaohua Li <shaohua.li@xxxxxxxxx> wrote: > Hi, > we are testing dbench benchmark and see big drop of 2.6.38-rc compared > to 2.6.37 in several machines with 2 sockets or 4 sockets. We have 12 > disks mount to /mnt/stp/dbenchdata/sd*/ and dbench runs against data of > the disks. According to perf, we saw more lock contentions: > In 2.6.37: 13.00% dbench [kernel.kallsyms] [k] _raw_spin_lock > In 2.6.38-rc: 69.45% dbench [kernel.kallsyms] [k]_raw_spin_lock > - 69.45% dbench [kernel.kallsyms] [k] _raw_spin_lock > - _raw_spin_lock > - 48.41% dput > - 61.17% path_put > - 60.47% do_path_lookup > + 53.18% user_path_at > + 42.13% do_filp_open > + 4.69% user_path_parent What filesystems are mounted on the path? > - 35.56% d_path > seq_path > show_vfsmnt > seq_read > vfs_read > sys_read > system_call_fastpath > __GI___libc_read This guy is from glibc's statvfs call that dbench uses. It parses /proc/mounts for mount flags which is racy (and not a good idea to do with any frequency). A patch went into the kernel that allows glibc to get the flags directly. Not sure about glibc status, I imagine it will get there in another decade or two... Can you try commenting it out of dbench source code? > + 2.17% do_filp_open > + 1.72% mounts_release > + 38.69% link_path_walk > + 30.21% path_get > + 19.08% nameidata_drop_rcu > + 0.83% __d_lookup > it appears there are heavy lock contention when dput release '/', 'mnt', > 'stp', 'dbenchdata' and 'proc' when dbench is running. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
