Folks,
When we upgraded arch xen/x86 to kernel 2.6.11, we noticed a slowdown
on a number of micro-benchmarks. In order to investigate, I built
native (non Xen) i686 uniprocessor kernels for 2.6.10 and 2.6.11 with
the same configuration and ran lmbench-3.0-a3 on them. The test
machine was a 2.4GHz Xeon box, gcc 3.3.3 (FC3 default) was used to
compile the kernels, NOHIGHMEM=y (2-level only).
On the i686 fork and exec benchmarks I found that there's been a
significant slowdown between 2.6.10 and 2.6.11. Some of the other
numbers a bit ugly too (see attached).
fork: 166 -> 235 (40% slowdown)
exec: 857 -> 1003 (17% slowdown)
I'm guessing this is down to the 4 level pagetables. This is rather a
surprise as I thought the compiler would optimise most of these
changes away. Apparently not.
Anyhow, this explains the arch Xen results we were seeing.
Results appended, median of 6 runs.
Best,
Ian
Processor, Processes - times in microseconds - smaller is better
------------------------------------------------------------------------------
Host OS Mhz null null open slct sig sig fork exec sh
call I/O stat clos TCP inst hndl proc proc proc
--------- ------------- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
commando- Linux 2.6.10 2400 0.49 0.57 2.06 3.06 19.6 0.89 2.70 166. 857. 2972
commando- Linux 2.6.11 2400 0.49 0.60 2.12 3.35 20.8 0.92 2.73 235. 1003 3168
Context switching - times in microseconds - smaller is better
-------------------------------------------------------------------------
Host OS 2p/0K 2p/16K 2p/64K 8p/16K 8p/64K 16p/16K 16p/64K
ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw
--------- ------------- ------ ------ ------ ------ ------ ------- -------
commando- Linux 2.6.10 7.5800 4.3300 8.1900 5.1100 33.1 8.37000 41.9
commando- Linux 2.6.11 7.9200 8.3200 8.3200 5.8300 26.6 9.46000 40.4
*Local* Communication latencies in microseconds - smaller is better
---------------------------------------------------------------------
Host OS 2p/0K Pipe AF UDP RPC/ TCP RPC/ TCP
ctxsw UNIX UDP TCP conn
--------- ------------- ----- ----- ---- ----- ----- ----- ----- ----
commando- Linux 2.6.10 7.750 19.4 21.3 37.2 45.5 42.5 53.2 76.
commando- Linux 2.6.11 7.920 20.3 23.6 40.2 50.1 46.5 57.6 87.
File & VM system latencies in microseconds - smaller is better
-------------------------------------------------------------------------------
Host OS 0K File 10K File Mmap Prot Page 100fd
Create Delete Create Delete Latency Fault Fault selct
--------- ------------- ------ ------ ------ ------ ------- ----- ------- -----
commando- Linux 2.6.10 39.3 16.2 92.7 35.2 122.0 1.200 2.14310 18.3
commando- Linux 2.6.11 40.8 16.8 99.5 36.7 163.0 1.075 2.27760 18.8
*Local* Communication bandwidths in MB/s - bigger is better
-----------------------------------------------------------------------------
Host OS Pipe AF TCP File Mmap Bcopy Bcopy Mem Mem
UNIX reread reread (libc) (hand) read write
--------- ------------- ---- ---- ---- ------ ------ ------ ------ ---- -----
commando- Linux 2.6.10 313. 440. 222. 1551.7 1528.5 549.1 566.8 1550 784.8
commando- Linux 2.6.11 554. 450. 224. 1564.8 1548.3 549.9 574.6 1528 760.5
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