Packet loss every 30.999 seconds

[Mark Fullmer]

Thanks, I'll test this later on today.

On Dec 19, 2007, at 1:11 PM, Kostik Belousov wrote:

> On Wed, Dec 19, 2007 at 09:13:31AM -0800, David G Lawrence wrote:
>>>> Try it with "find / -type f >/dev/null" to duplicate the problem
>>>> almost
>>>> instantly.
>>>
>>> I was able to verify last night that (cd /; tar -cpf -) > all.tar  
>>> would
>>> trigger the problem.  I'm working getting a test running with
>>> David's ffs_sync() workaround now, adding a few counters there  
>>> should
>>> get this narrowed down a little more.
>>
>>    Unfortunately, the version of the patch that I sent out isn't  
>> going to
>> help your problem. It needs to yield at the top of the loop, but  
>> vp isn't
>> necessarily valid after the wakeup from the msleep. That's a  
>> problem that
>> I'm having trouble figuring out a solution to - the solutions that  
>> come
>> to mind will all significantly increase the overhead of the loop.
>>    As a very inadequate work-around, you might consider lowering
>> kern.maxvnodes to something like 20000 - that might be low enough to
>> not trigger the problem, but also be high enough to not significantly
>> affect system I/O performance.
>
> I think the following may be safe. It counts only the clean scanned  
> vnodes
> and does not evaluate the vp, that indeed may be reclaimed, after  
> the sleep.
>
> I never booted with the change.
>
> diff --git a/sys/ufs/ffs/ffs_vfsops.c b/sys/ufs/ffs/ffs_vfsops.c
> index cbccc62..e686b97 100644
> --- a/sys/ufs/ffs/ffs_vfsops.c
> +++ b/sys/ufs/ffs/ffs_vfsops.c
> @@ -1176,6 +1176,7 @@ ffs_sync(mp, waitfor, td)
>  	struct ufsmount *ump = VFSTOUFS(mp);
>  	struct fs *fs;
>  	int error, count, wait, lockreq, allerror = 0;
> +	int yield_count;
>  	int suspend;
>  	int suspended;
>  	int secondary_writes;
> @@ -1216,6 +1217,7 @@ loop:
>  	softdep_get_depcounts(mp, &softdep_deps, &softdep_accdeps);
>  	MNT_ILOCK(mp);
>
> +	yield_count = 0;
>  	MNT_VNODE_FOREACH(vp, mp, mvp) {
>  		/*
>  		 * Depend on the mntvnode_slock to keep things stable enough
> @@ -1233,6 +1235,11 @@ loop:
>  		    (IN_ACCESS | IN_CHANGE | IN_MODIFIED | IN_UPDATE)) == 0 &&
>  		    vp->v_bufobj.bo_dirty.bv_cnt == 0)) {
>  			VI_UNLOCK(vp);
> +			if (yield_count++ == 500) {
> +				yield_count = 0;
> +				msleep(&yield_count, MNT_MTX(mp), PZERO,
> +				    "ffspause", 1);
> +			}
>  			continue;
>  		}
>  		MNT_IUNLOCK(mp);