linux-kernel - Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount

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Date:	Tue, 3 Sep 2013 09:24:06 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Waiman Long <waiman.long@...com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jeff Layton <jlayton@...hat.com>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless
 update of refcount

On Tue, Sep 3, 2013 at 8:01 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Waiman Long <waiman.long@...com> wrote:
>
>> On 08/30/2013 10:42 PM, Al Viro wrote:
>> >On Sat, Aug 31, 2013 at 03:35:16AM +0100, Al Viro wrote:
>> >
>> >>Aha...  OK, I see what's going on.  We end up with shm_mnt *not* marked
>> >>as long-living vfsmount, even though it lives forever.  See if the
>> >>following helps; if it does (and I very much expect it to), we want to
>> >>put it in -stable.  As it is, you get slow path in mntput() each time
>> >>a file created by shmem_file_setup() gets closed.  For no reason whatsoever...
>> >We still want MS_NOUSER on shm_mnt, so we'd better make sure that
>> >shmem_fill_super() sets it on the internal instance...  Fixed variant
>> >follows:
>> >
>> >Signed-off-by: Al Viro<viro@...iv.linux.org.uk>
>> >diff --git a/mm/shmem.c b/mm/shmem.c
>> >index e43dc55..5261498 100644
>> >--- a/mm/shmem.c
>> >+++ b/mm/shmem.c
>> >@@ -2615,13 +2615,15 @@ int shmem_fill_super(struct super_block *sb, void *data, int silent)
>> >      * tmpfs instance, limiting inodes to one per page of lowmem;
>> >      * but the internal instance is left unlimited.
>> >      */
>> >-    if (!(sb->s_flags&  MS_NOUSER)) {
>> >+    if (!(sb->s_flags&  MS_KERNMOUNT)) {
>> >             sbinfo->max_blocks = shmem_default_max_blocks();
>> >             sbinfo->max_inodes = shmem_default_max_inodes();
>> >             if (shmem_parse_options(data, sbinfo, false)) {
>> >                     err = -EINVAL;
>> >                     goto failed;
>> >             }
>> >+    } else {
>> >+            sb->s_flags |= MS_NOUSER;
>> >     }
>> >     sb->s_export_op =&shmem_export_ops;
>> >     sb->s_flags |= MS_NOSEC;
>> >@@ -2831,8 +2833,7 @@ int __init shmem_init(void)
>> >             goto out2;
>> >     }
>> >
>> >-    shm_mnt = vfs_kern_mount(&shmem_fs_type, MS_NOUSER,
>> >-                             shmem_fs_type.name, NULL);
>> >+    shm_mnt = kern_mount(&shmem_fs_type);
>> >     if (IS_ERR(shm_mnt)) {
>> >             error = PTR_ERR(shm_mnt);
>> >             printk(KERN_ERR "Could not kern_mount tmpfs\n");
>>
>> Yes, that patch worked. It eliminated the lglock as a bottleneck in
>> the AIM7 workload. The lg_global_lock did not show up in the perf
>> profile, whereas the lg_local_lock was only 0.07%.
>
> Just curious: what's the worst bottleneck now in the optimized kernel? :-)
>
> Thanks,
>
>         Ingo

Can someone summarize this thread (70+ postings)?
Which patches are needed? And fixing what?
( Can people provide separate patches with a proper changelog? )
Improvements?


Thanks.

- Sedat (still struggling with perf) -
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