Date: Sat, 14 Apr 2018 07:14:17 +0200 From: =?UTF-8?Q?Niels_Kobsch=c3=a4tzki?= <niels@kobschaetzki.net> To: Rick Macklem <rmacklem@uoguelph.ca>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Re: High rate of NFS cache misses after upgrading from 10.3-prerelease to 11.1-release Message-ID: <f3cea179-75d7-916b-68d1-61fe75c0bb80@kobschaetzki.net> In-Reply-To: <YQBPR0101MB1042D2F0CE2575EB4F17588ADDB20@YQBPR0101MB1042.CANPRD01.PROD.OUTLOOK.COM> References: <ce3712c0-626e-c8f2-3bba-933cf359bcef@kobschaetzki.net> <YQBPR0101MB1042D2F0CE2575EB4F17588ADDB20@YQBPR0101MB1042.CANPRD01.PROD.OUTLOOK.COM>
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On 04/14/2018 03:49 AM, Rick Macklem wrote: > Niels Kobschätzki wrote: >> sorry for the cross-posting but so far I had no real luck on the forum >> or on question, thus I want to try my luck here as well. > I read email lists but don't do the other stuff, so I just saw this yesterday. > Short answer, I haven't a clue why cache hits rate would have changed. > > The code that decides if there is a hit/miss for the attribute cache is in > ncl_getattrcache() and the code hasn't changed between 10.3->11.1, > except the old code did a mtx_lock(&Giant), but I can't imagine how that > would affect the code. > > You might want to: > # sysctl -a | fgrep vfs.nfs > for both the 10.3 and 11.1 systems, to check if any defaults have somehow > been changed. (I don't recall any being changed, but??) I did that and there did nothing change. > If you go into ncl_getattrcache() {it's in sys/fs/nfsclient/nfs_clsubs.c} > and add a printf() for "time_second" and "np->n_mtime.tv_sec" near the > top, where it calculates "timeo" from it. > Running this hacked kernel might show you if either of these fields is bogus. > (You could then printf() "timeo" and "np->n_attrtimeo" just before the "if" > clause that increments "attrcache_misses", which is where the cache misses > happen to see why it is missing the cache.) > If you could do this for the 10.3 kernel as well, this might indicate why the > miss rate has increased? I will do this next week. On monday we switch for other reasons to other nfs-servers and when we see that they run stable, I will do this next. Btw. I calculated now the percentages. The old servers had a attr miss rate of something like 0.004%, while the upgraded one has more like 2.7%. This is till low from what I've read (I remember that you should start adjusting acreg* when you hit more than 40% misses) but far higher than before. nfsstat -c for one of the working servers looks like this (I did a -cz before to reset it and did this a couple of seconds later): Attr Hits Misses Lkup Hits Misses BioR Hits Misses BioW Hits Misses 10085375 255 9163995 577 540 0 0 0 BioRLHits Misses BioD Hits Misses DirE Hits Misses Accs Hits Misses 1380 0 0 0 0 0 9169427 277 and for the non-working server: Attr Hits Misses Lkup Hits Misses BioR Hits Misses BioW Hits Misses 1606365 20647 1418205 239 581 0 0 0 BioRLHits Misses BioD Hits Misses DirE Hits Misses Accs Hits Misses 895 0 0 0 0 0 1439080 337 >> I upgraded a machine from 10.3-Prerelease (custom kernel with >> tcp_fastopen added) to 11.1-Release (standard kernel) with >> freebsd-update. I have two other machines that are still on >> 10.3-Prerelease. Those machines mount an NFS-export from a >> Linux-NFS-server and use NFSv3. The machine that got upgraded shows now >> far more cache misses for getattr than on the 10.3-machines (we talk a >> factor of 100) in munin. munin also shows a lot more cache-misses for >> other metrics like biow, biorl, biod (where can I find what those >> metrics mean…currently I have not even an understanding what these are) >> etc. >> >> Can anybody help me how I can debug this problem or has an idea what >> could cause the problem? The result of this behavior is that this >> machine shows a lower performance than the others and I cannot upgrade >> other machines before I didn't fix this bug. > I haven't run a 10.x system in quite a while. When I get home in a few days, > I might be able to reproduce this. If I can. I can poke at it, but it would be at > least a week before I might have an answer and I may not figure it out for a > long time. Ok, thanks a lot. That would be great. Niels
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