[squid-users] Help Needed: Any suggestion on performance downgrade after enable Cache Digest?

Hi,

Recently I did some interesting performance testing on the Squid configured
with Cache Digest Enabled. The testing result shows that the Squid use more
than 20% CPU time than the Squid running without Cache Digest. Following are
my detailed testing environment and configuration and result. Anyone can
give me some light on the possible reason will be greatly appreciated.
Please also point out the possible configuration errors if any. Thanks a
lot.

1. Hardware configuration : HP DL380
(1) Squid Server
CPU: 2 Xeon 2.8GHz CPUs, each Xeon CPU has 2 Cores
Memory size: 6G, Disk: 36G, NIC: 1000M
(2) Client and Web Server : Dell Vostro200 running with Web Polygraph 3.1.5

2. Squid Configuration
(1) 2 Squid instances are running on the same HP server, each using same IP
address but different PORT, pure in memory cache
Squid1 configuration:
http_port 8081
cache_mem 1024 MB
cache_dir null /tmp
cache_peer 192.168.10.2 sibling 8082 0 proxy-only
digest_generation on
digest_bits_per_entry 5
digest_rebuild_period 1 hour
digest_swapout_chunk_size 4096 bytes
digest_rebuild_chunk_percentage 10

Squid2 configuration:
http_port 8082
cache_mem 1024 MB
cache_dir null /tmp
cache_peer 192.168.10.2 sibling 8081 0 proxy-only
digest_generation on
digest_bits_per_entry 5
digest_rebuild_period 1 hour
digest_swapout_chunk_size 4096 bytes
digest_rebuild_chunk_percentage 10

3. 2 Polygraph Clients are used to send HTTP requests to Squid instances.
Different client send request to different Squid instance. Each client
configures 1000 users with 1.2 request/s, so totally each client send 1200
requests/s.

4. Test result (Note: since 4 CPU used on the server, the total CPU
utilization is 400%)
(1) Running 2 Squid instances with Cache Digest Enabled, each handles 1200
request/second:
Each instance used ~95% CPU even during the time Squid didn't rebuild the
digest

(2) Running 2 Squid instances with Cache Digest Enabled, one handles 1200
request/second, one is idle(no traffic to it)
The one with traffic has CPU utilization ~65%, the other one is idle

(3) Running 2 Squid instances with Cache Digest Disabled, each handles 1200
request/second:
Each instance used ~75% CPU

Best Regards,
Bo Zhou
Received on Tue Apr 22 2008 - 13:30:15 MDT