Messages in this thread Patch in this message | | | Date | Tue, 21 Aug 2012 15:54:54 -0500 | From | Nathan Zimmer <> | Subject | [RFC] Move kfree outside pde_unload_lock |
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I am currently tracking a hotlock reported by a customer on a large, 512 cores, system, I am currently running 3.6.0 rc1 but the issue looks like it has been this way for a very long time. The offending lock is proc_dir_entry->pde_unload_lock.
In proc_reg_release we are doing a kfree under the spinlock which is ok but it means we are holding the lock longer then required. Scaling improved when I moved kfree out.
Also shouldn't the comment on pde_unload_lock also note that pde_openers and pde_unload_completion are both used under the lock?
Here is some data from quick test program which just reads from /proc/cpuinfo. Lower is better, as you can see the worst case scenario is improved. baseline moved kfree tasks read-sec read-sec 1 0.0141 0.0141 2 0.0140 0.0140 4 0.0140 0.0141 8 0.0145 0.0145 16 0.0553 0.0548 32 0.1688 0.1622 64 0.5017 0.3856 128 1.7005 0.9710 256 5.2513 2.6519 512 8.0529 6.2976
If the patch looks agreeable I will resend it properly.
diff --git a/fs/proc/inode.c b/fs/proc/inode.c index 7ac817b..46016c1 100644 --- a/fs/proc/inode.c +++ b/fs/proc/inode.c @@ -403,9 +403,11 @@ static int proc_reg_release(struct inode *inode, struct file *file) release = pde->proc_fops->release; if (pdeo) { list_del(&pdeo->lh); - kfree(pdeo); } spin_unlock(&pde->pde_unload_lock); + if (pdeo) { + kfree(pdeo); + } if (release) rv = release(inode, file);
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