Xen users - May 2007 - Apache CGI Performance Big Degration in Dom0 vs. Native

Hi there,

I ran a test on an Apache server, the workload is a helloworld.c compiled cgi,
very simple. OS is SLES 10. The stress tool is ab (apache bench).

The performance looks big degration from native to Dom0:

Running in prefork mode:

                                       Native                              Dom0
Performance(request/s)   3700                                 . 650
CPU%                             75%                                  99%



Running in worker mode:
                                       Native                              Dom0
Performance(request/s)     1750.                               769
CPU%                             32%                                 26%


Also running XenOprof and Oprof as below clock cycles data:

Domain 0, worker:
CPU: Core 2, speed 2666.75 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask
of 0x00 (Unhalted core cycles) count 100000
samples  %        image name               app name                 symbol name
71855     4.6699  xen-syms-pae-3.0.4_13138-0.33 xen-syms-pae-3.0.4_13138-0.33
get_page_from_l1e
71812     4.6672  xen-syms-pae-3.0.4_13138-0.33 xen-syms-pae-3.0.4_13138-0.33
handle_exception
58634     3.8107  xen-syms-pae-3.0.4_13138-0.33 xen-syms-pae-3.0.4_13138-0.33
put_page_from_l1e
56301     3.6591  xen-syms-pae-3.0.4_13138-0.33 xen-syms-pae-3.0.4_13138-0.33
do_update_va_mapping
49543     3.2199  vmlinux-2.6.16.46-0.10-xenpae vmlinux-2.6.16.46-0.10-xenpae
_spin_lock

Domain 0, Prefork:
CPU: Core 2, speed 2666.75 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask
of 0x00 (Unhalted core cycles) count 100000
samples  %        image name               app name                 symbol name
492796   20.0510  xen-syms-pae-3.0.4_13138-0.33 xen-syms-pae-3.0.4_13138-0.33
do_update_va_mapping
268506   10.9251  xen-syms-pae-3.0.4_13138-0.33 xen-syms-pae-3.0.4_13138-0.33
ptwr_do_page_fault
81074     3.2988  xen-syms-pae-3.0.4_13138-0.33 xen-syms-pae-3.0.4_13138-0.33
test_all_events
72424     2.9468  xen-syms-pae-3.0.4_13138-0.33 xen-syms-pae-3.0.4_13138-0.33
get_page_from_l1e
66056     2.6877  xen-syms-pae-3.0.4_13138-0.33 xen-syms-pae-3.0.4_13138-0.33
handle_exception
61031     2.4832  xen-syms-pae-3.0.4_13138-0.33 xen-syms-pae-3.0.4_13138-0.33
do_mmu_update

Native, Worker:
CPU: Core 2, speed 2667.14 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask
of 0x00 (Unhalted core cycles) count 100000
samples  %        app name                 symbol name
46048     5.8715  vmlinux-2.6.16.46-0.10-bigsmp kmap_atomic
41587     5.3027  vmlinux-2.6.16.46-0.10-bigsmp copy_page_range
39759     5.0696  vmlinux-2.6.16.46-0.10-bigsmp unmap_vmas
38722     4.9373  vmlinux-2.6.16.46-0.10-bigsmp page_fault
30638     3.9066  vmlinux-2.6.16.46-0.10-bigsmp page_remove_rmap
29481     3.7591  vmlinux-2.6.16.46-0.10-bigsmp __handle_mm_fault


Native Prefork:
CPU: Core 2, speed 2667.14 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask
of 0x00 (Unhalted core cycles) count 100000
samples  %        app name                 symbol name
47505     6.9430  vmlinux-2.6.16.46-0.10-bigsmp kmap_atomic
41182     6.0189  vmlinux-2.6.16.46-0.10-bigsmp page_fault
36425     5.3236  vmlinux-2.6.16.46-0.10-bigsmp copy_page_range
34533     5.0471  vmlinux-2.6.16.46-0.10-bigsmp unmap_vmas
32155     4.6996  vmlinux-2.6.16.46-0.10-bigsmp __handle_mm_fault
30848     4.5085  vmlinux-2.6.16.46-0.10-bigsmp find_get_page
28589     4.1784  vmlinux-2.6.16.46-0.10-bigsmp page_remove_rmap

On pure HTML workload, I find little performance gap between domain 0 and
Native, and neither so much Memory and Page operation.
Is the Domain 0 performance for CGI degration because of Xen Memory and Page
ineffiencency? Any hints or experience on this?


thanks in advance

Rgds
Hunter Tang


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