Re: Res: [squid-users] squid 3.2.0.5 smp scaling issues

Ok, I finally got a chance to test 2.7STABLE9

it performs about the same as squid 3.0, possibly a little better.

with my somewhat stripped down config (smaller regex patterns, replacing
CIDR blocks and names that would need to be looked up in /etc/hosts with
individual IP addresses)

2.7 gives ~4800 requests/sec
3.0 gives ~4600 requests/sec
3.2.0.6 with 1 worker gives ~1300 requests/sec
3.2.0.6 with 5 workers gives ~2800 requests/sec

the numbers for 3.0 are slightly better than what I was getting with the
full ruleset, but the numbers for 3.2.0.6 are pretty much exactly what I
got from the last round of tests (with either the full or simplified
ruleset)

so 3.1 and 3.2 are a very significant regression from 2.7 or 3.0, and the
ability to use multiple worker processes in 3.2 doesn't make up for this.

the time taken seems to almost all be in the ACL avaluation as eliminating
all the ACLs takes 1 worker with 3.2 up to 4200 requests/sec.

one theory is that even though I have IPv6 disabled on this build, the
added space and more expensive checks needed to compare IPv6 addresses
instead of IPv4 addresses accounts for the single worker drop of ~66%.
that seems rather expensive, even though there are 293 http_access lines
(and one of them uses external file contents in it's acls, so it's a total
of ~2400 source/destination pairs, however due to the ability to shortcut
the comparison the number of tests that need to be done should be <400)

In addition, there seems to be some sort of locking betwen the multiple
worker processes in 3.2 when checking the ACLs as the test with almost no
ACLs scales close to 100% per worker while with the ACLs it scales much
more slowly, and above 4-5 workers actually drops off dramatically (to the
point where with 8 workers the throughput is down to about what you get
with 1-2 workers) I don't see any conceptual reason why the ACL checks of
the different worker threads should impact each other in any way, let
alone in a way that limits scalability to ~4 workers before adding more
workers is a net loss.

David Lang

> On Wed, 13 Apr 2011, Marcos wrote:
>
>> Hi David,
>>
>> could you run and publish your benchmark with squid 2.7 ???
>> i'd like to know if is there any regression between 2.7 and 3.x series.
>>
>> thanks.
>>
>> Marcos
>>
>>
>> ----- Mensagem original ----
>> De: "david_at_lang.hm" <david_at_lang.hm>
>> Para: Amos Jeffries <squid3_at_treenet.co.nz>
>> Cc: squid-users_at_squid-cache.org; squid-dev_at_squid-cache.org
>> Enviadas: S?bado, 9 de Abril de 2011 12:56:12
>> Assunto: Re: [squid-users] squid 3.2.0.5 smp scaling issues
>>
>> On Sat, 9 Apr 2011, Amos Jeffries wrote:
>>
>>> On 09/04/11 14:27, david_at_lang.hm wrote:
>>>> A couple more things about the ACLs used in my test
>>>>
>>>> all of them are allow ACLs (no deny rules to worry about precidence of)
>>>> except for a deny-all at the bottom
>>>>
>>>> the ACL line that permits the test source to the test destination has
>>>> zero overlap with the rest of the rules
>>>>
>>>> every rule has an IP based restriction (even the ones with url_regex are
>>>> source -> URL regex)
>>>>
>>>> I moved the ACL that allows my test from the bottom of the ruleset to
>>>> the top and the resulting performance numbers were up as if the other
>>>> ACLs didn't exist. As such it is very clear that 3.2 is evaluating every
>>>> rule.
>>>>
>>>> I changed one of the url_regex rules to just match one line rather than
>>>> a file containing 307 lines to see if that made a difference, and it
>>>> made no significant difference. So this indicates to me that it's not
>>>> having to fully evaluate every rule (it's able to skip doing the regex
>>>> if the IP match doesn't work)
>>>>
>>>> I then changed all the acl lines that used hostnames to have IP
>>>> addresses in them, and this also made no significant difference
>>>>
>>>> I then changed all subnet matches to single IP address (just nuked /##
>>>> throughout the config file) and this also made no significant difference.
>>>>
>>>
>>> Squid has always worked this way. It will *test* every rule from the top
>>> down to the one that matches. Also testing each line left-to-right until
>>> one fails or the whole line matches.
>>>
>>>>
>>>> so why are the address matches so expensive
>>>>
>>>
>>> 3.0 and older IP address is a 32-bit comparison.
>>> 3.1 and newer IP address is a 128-bit comparison with memcmp().
>>>
>>> If something like a word-wise comparison can be implemented faster than
>>> memcmp() we would welcome it.
>>
>> I wonder if there should be a different version that's used when IPv6 is
>> disabled. this is a pretty large hit.
>>
>> if the data is aligned properly, on a 64 bit system this should still only
>> be 2 compares. do you do any alignment on the data now?
>>
>>>> and as noted in the e-mail below, why do these checks not scale nicely
>>>> with the number of worker processes? If they did, the fact that one 3.2
>>>> process is about 1/3 the speed of a 3.0 process in checking the acls
>>>> wouldn't matter nearly as much when it's so easy to get an 8+ core
>>>> system.
>>>>
>>>
>>> There you have the unknown.
>>
>> I think this is a fairly critical thing to figure out.
Received on Fri Apr 15 2011 - 03:06:17 MDT