On Wed, Sep 14, 2005 at 11:17:42PM +0200, Eric Dumazet wrote:
> In SMP (and NUMA) environnements, each time a thread wants to open or close
> a file, it has to acquire the spinlock, thus invalidating the cache line
> containing this spinlock on other CPUS. So other threads doing
> read()/write()/... calls that use RCU to access the file table are going to
> ask further memory (possibly NUMA) transactions to read again this memory
> line.
>
> Please consider applying this patch. It moves the spinlock to another cache
> line, so that concurrent threads can share the cache line containing
> 'count' and 'fdt' fields.
>
> --- linux-2.6.14-rc1/include/linux/file.h 2005-09-13 05:12:09.000000000 +0200
> +++ linux-2.6.14-rc1-ed/include/linux/file.h 2005-09-15 01:09:13.000000000 +0200
> @@ -34,12 +34,12 @@
> */
> struct files_struct {
> atomic_t count;
> - spinlock_t file_lock; /* Protects all the below members. Nests inside tsk->alloc_lock */
> struct fdtable *fdt;
> struct fdtable fdtab;
> fd_set close_on_exec_init;
> fd_set open_fds_init;
> struct file * fd_array[NR_OPEN_DEFAULT];
> + spinlock_t file_lock; /* Protects concurrent writers. Nests inside tsk->alloc_lock */
> };
>
> #define files_fdtable(files) (rcu_dereference((files)->fdt))
For most apps without too many open fds, the embedded fd_sets
are going to be used. Wouldn't that mean that open()/close() will
invalidate the cache line containing fdt, fdtab by updating
the fd_sets ? If so, you optimization really doesn't help.
Thanks
Dipankar
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
| |
 |