Re: Excessive context switching on SMP Xeons

Bill Montgomery wrote:
> All,
>
> I realize the excessive-context-switching-on-xeon issue has been
> discussed at length in the past, but I wanted to follow up and verify my
> conclusion from those discussions:
>
> On a 2-way or 4-way Xeon box, there is no way to avoid excessive
> (30,000-60,000 per second) context switches when using PostgreSQL 7.4.5
> to query a data set small enough to fit into main memory under a
> significant load.
>
> I am experiencing said symptom on two different dual-Xeon boxes, both
> Dells with ServerWorks chipsets, running the latest RH9 and RHEL3
> kernels, respectively. The databases are 90% read, 10% write, and are
> small enough to fit entirely into main memory, between pg shared buffers
> and kernel buffers.
>

I don't know if my box is not loaded enough but I have a dual-Xeon box,
by DELL with the HT enabled and I'm not experiencing this kind of CS
problem, normaly hour CS is around 100000 per second.

# cat /proc/version
Linux version 2.4.9-e.24smp (bhcompile(at)porky(dot)devel(dot)redhat(dot)com) (gcc version 2.96 20000731 (Red Hat Linux 7.2 2.96-118.7.2)) #1 SMP Tue May 27 16:07:39 EDT 2003

# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.80GHz
stepping : 7
cpu MHz : 2787.139
cache size : 512 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips : 5557.45

processor : 1
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.80GHz
stepping : 7
cpu MHz : 2787.139
cache size : 512 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips : 5570.56

processor : 2
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.80GHz
stepping : 7
cpu MHz : 2787.139
cache size : 512 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips : 5570.56

processor : 3
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.80GHz
stepping : 7
cpu MHz : 2787.139
cache size : 512 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips : 5570.56

Regards
Gaetano Mendola