Packet loss every 30.999 seconds

[Mark Fullmer]

Thanks.  Have a kernel building now.  It takes about a day of uptime  
after reboot before I'll see the problem.

--
mark

On Dec 17, 2007, at 5:24 AM, David G Lawrence wrote:

>> While trying to diagnose a packet loss problem in a RELENG_6 snapshot
>> dated
>> November 8, 2007 it looks like I've stumbled across a broken  
>> driver or
>> kernel routine which stops interrupt processing long enough to  
>> severly
>> degrade network performance every 30.99 seconds.
>
>    I noticed this as well some time ago. The problem has to do with  
> the
> processing (syncing) of vnodes. When the total number of allocated  
> vnodes
> in the system grows to tens of thousands, the ~31 second periodic sync
> process takes a long time to run. Try this patch and let people  
> know if
> it helps your problem. It will periodically wait for one tick (1ms)  
> every
> 500 vnodes of processing, which will allow other things to run.
>
> Index: ufs/ffs/ffs_vfsops.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/ufs/ffs/ffs_vfsops.c,v
> retrieving revision 1.290.2.16
> diff -c -r1.290.2.16 ffs_vfsops.c
> *** ufs/ffs/ffs_vfsops.c	9 Oct 2006 19:47:17 -0000	1.290.2.16
> --- ufs/ffs/ffs_vfsops.c	25 Apr 2007 01:58:15 -0000
> ***************
> *** 1109,1114 ****
> --- 1109,1115 ----
>   	int softdep_deps;
>   	int softdep_accdeps;
>   	struct bufobj *bo;
> + 	int flushed_count = 0;
>
>   	fs = ump->um_fs;
>   	if (fs->fs_fmod != 0 && fs->fs_ronly != 0) {		/* XXX */
> ***************
> *** 1174,1179 ****
> --- 1175,1184 ----
>   			allerror = error;
>   		vput(vp);
>   		MNT_ILOCK(mp);
> + 		if (flushed_count++ > 500) {
> + 			flushed_count = 0;
> + 			msleep(&flushed_count, MNT_MTX(mp), PZERO, "syncw", 1);
> + 		}
>   	}
>   	MNT_IUNLOCK(mp);
>   	/*
>
> -DG
>
> David G. Lawrence
> President
> Download Technologies, Inc. - http://www.downloadtech.com - (866)  
> 399 8500
> The FreeBSD Project - http://www.freebsd.org
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