[squid-users] Squid3: 100 % CPU load during object caching

Fri Jul 24 05:54:57 UTC 2015

It is not easy for me, but I have tested Squid 3.3.8 from the Ubuntu packaging on a "real" physical infrastructure. I get the same results on the physical machine (1x Intel(R) Xeon(R) CPU E3-1225 V2 @ 3.20GHz, 32 GB RAM, 1 TB disk) where Squid is running: 100 % CPU usage, 500 KB/sec download rate. All machines are idle and we have 1 GBit ethernet.

The strace log from the physical test scenario can be found here, but I think it does not differ from the "virtual" test scenario:
http://wikisend.com/download/293856/squid.strace2

@Marcus:
Have you verified that the file does not fit into memory and gets cached on disk? On which OS is Squid running? What are your build options of Squid (squid -v)? Is it possible that the issue is not part of 3.4.12? Do we have a regression?

@Amos, Eliezer
Is someone able to reproduce the disk caching effect?

Regards,
Jens

Gesendet: Donnerstag, 23. Juli 2015 um 20:08 Uhr
Von: "Marcus Kool" <marcus.kool at urlfilterdb.com>
An: "Jens Offenbach" <wolle5050 at gmx.de>, "Amos Jeffries" <squid3 at treenet.co.nz>, "Eliezer Croitoru" <eliezer at ngtech.co.il>, squid-users at lists.squid-cache.org
Betreff: Re: Aw: Re: [squid-users] Squid3: 100 % CPU load during object caching
The strace output shows this loop:

Squid reads 16K-1 bytes from FD 13 webserver
Squid writes 4 times 4K to FD 17 /var/cache/squid3/00/00/00000000
Squid writes 4 times 4K to FD 12 browser

But this loop does not explain the 100% CPU usage...

Does Squid do a buffer reshuffle when it reads 16K-1 and writes 16K ?

I did the download test with Squid 3.4.12 AUFS on an idle system with a 500 mbit connection and 1 CPU with 4 cores @ 3.7 GHz.
The first download used 35% of 1 CPU core with a steady download speed of 62 MB/sec.
The second (cached) download used 50% of 1 CPU core with a steady download speed of 87 MB/sec.
I never looked at Squid CPU usage and do not know what is reasonable but it feels high.

With respect to the 100% CPU issue of Jens, one factor is that Squid runs in a virtual machine.
Squid in a virtual machine cannot be compared with a wget test since Squid allocates a lot of memory that the host must manage.
This is a possible explanation for the fact that you see the performance going down and up.
Can you do the same test on the host (i.e. not inside a VM).

Marcus

On 07/23/2015 10:39 AM, Jens Offenbach wrote:
> I have attached strace to Squid and waited until the download rate has decreased to 500 KB/sec.
> I used "cache_dir aufs /var/cache/squid3 88894 16 256 max-size=10737418240".
> Here is the download link:
> http://w1.wikisend.com/node-fs/download/6a004a416f65b4cdf7f8eff4ff961199/squid.strace
> I hope it can help you.
> *Gesendet:* Donnerstag, 23. Juli 2015 um 13:29 Uhr
> *Von:* "Marcus Kool" <marcus.kool at urlfilterdb.com>
> *An:* "Jens Offenbach" <wolle5050 at gmx.de>, "Eliezer Croitoru" <eliezer at ngtech.co.il>, "Amos Jeffries" <squid3 at treenet.co.nz>, squid-users at lists.squid-cache.org
> *Betreff:* Re: [squid-users] Squid3: 100 % CPU load during object caching
> I am not sure if it is relevant, maybe it is:
>
> I am developing an ICAP daemon and after the ICAP server sends a "100 continue"
> Squid sends the object to the ICAP server in small chunks of varying sizes:
> 4095, 5813, 1448, 4344, 1448, 1448, 2896, etc.
> Note that the interval of receiving the chunks is 1/1000th of a second.
> It seems that Squid forwards the object to the ICAP server every time it receives
> one or a few TCP packets.
>
> I have a suspicion that in the scenario of 100% CPU, large #write calls and low throughput a similar thing is happening:
> Squid physically stores a small part of the object many times, i.e. every time one or a few TCP packets arrive.
>
> Amos, is there a debug setting that can confirm/reject this suspicion?
>
> Marcus
>
>
> On 07/23/2015 04:25 AM, Jens Offenbach wrote:
> > A test with ROCK "cache_dir rock /var/cache/squid3 51200" gives very confusing results.
> >
> > I cleared the cache:
> > rm -rf /var/cache/squid3/*
> > squid -z
> > squid
> > http_proxy=http://139.2.57.120:3128/[http://139.2.57.120:3128/] wget http://test-server/freesurfer-Linux-centos6_x86_64-stable-pub-v5.3.0.tar
> >
> > The download starts with 10 MB/sec and stays constant for 1 minutes, then it drops gradually to 1 MB/sec and stays there for some time. After 5 minutes the download rate returns back to 10 MB/sec
> very quickly and drops again step-by-step to 1 MB/sec. After 5-6 minutes the download rates rises again to 10 MB/sec and drops again gradually to 1 MB/sec.
> >
> > During caching progress, we have 100 % CPU usage and a disk IO that is corresponds with the download rate.
> >
> > For further investigations I give you my build properties:
> > squid -v
> > Squid Cache: Version 3.5.6
> > Service Name: squid
> > configure options: '--build=x86_64-linux-gnu' '--prefix=/usr' '--includedir=/include' '--mandir=/share/man' '--infodir=/share/info' '--sysconfdir=/etc' '--localstatedir=/var'
> '--libexecdir=/lib/squid3' '--srcdir=.' '--disable-maintainer-mode' '--disable-dependency-tracking' '--disable-silent-rules' '--datadir=/usr/share/squid3' '--sysconfdir=/etc/squid3'
> '--mandir=/usr/share/man' '--enable-inline' '--enable-async-io=8' '--enable-storeio=ufs,aufs,diskd,rock' '--enable-removal-policies=lru,heap' '--enable-delay-pools' '--enable-cache-digests'
> '--enable-underscores' '--enable-icap-client' '--enable-follow-x-forwarded-for' '--enable-auth-basic=DB,fake,getpwnam,LDAP,NCSA,NIS,PAM,POP3,RADIUS,SASL,SMB' '--enable-auth-digest=file,LDAP'
> '--enable-auth-negotiate=kerberos,wrapper' '--enable-auth-ntlm=fake,smb_lm' '--enable-external-acl-helpers=file_userip,kerberos_ldap_group,LDAP_group,session,SQL_session,unix_group,wbinfo_group'
> '--enable-url-rewrite-helpers=fake' '--enable-eui' '--enable-e
> s
> i' '--enable-icmp' '--enable-zph-qos' '--enable-ecap' '--disable-translation' '--with-swapdir=/var/cache/squid3' '--with-logdir=/var/log/squid3' '--with-pidfile=/var/run/squid3.pid'
> '--with-filedescriptors=65536' '--with-large-files' '--with-default-user=proxy' '--enable-linux-netfilter' 'build_alias=x86_64-linux-gnu' 'CFLAGS=-g -O2 -fPIE -fstack-protector
> --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall' 'LDFLAGS=-Wl,-Bsymbolic-functions -fPIE -pie -Wl,-z,relro -Wl,-z,now' 'CPPFLAGS=-D_FORTIFY_SOURCE=2' 'CXXFLAGS=-g -O2 -fPIE
> -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security'
> >
> >
> > Gesendet: Mittwoch, 22. Juli 2015 um 21:47 Uhr
> > Von: "Eliezer Croitoru" <eliezer at ngtech.co.il>
> > An: squid-users at lists.squid-cache.org
> > Betreff: Re: [squid-users] Squid3: 100 % CPU load during object caching
> > On 22/07/2015 21:59, Eliezer Croitoru wrote:
> >> Hey Jens,
> >>
> >> I have tested the issue with LARGE ROCK and not AUFS or UFS.
> >> Using squid or not my connection to the server is about 2.5 MBps (20Mbps).
> >> Squid is sitting on an intel atom with SSD drive and on a HIT case the
> >> download speed is more then doubled to 4.5 MBps(36Mbps).
> >> I have not tried it with AUFS yet.
> >
> >
> > And I must admit that AUFS beats rock cache with speed.
> > I have tried rock with basic "cache_dir rock /var/spool/squid 8000" vs
> > "cache_dir aufs /var/spool/squid 8000 16 256" and the aufs cache HIT
> > results more then doubles 3 the speed rock gave with default settings.
> >
> > So about 15MBps which is 120Mbps.
> > I do not seem to feel what Jens feels but the 100% CPU might be because
> > of spinning disk hangs while reading the file from disk.
> >
> > Amos, I remember that there were some suggestions how to tune large rock.
> > Any hints?
> > I can test it and make it a suggestion for big files.
> >
> > Eliezer
> >
> > _______________________________________________
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