Date: Sun, 26 Apr 2009 19:27:42 -0700 From: Garrett Cooper <yanefbsd@gmail.com> To: Pieter de Goeje <pieter@degoeje.nl> Cc: acpi <acpi@freebsd.org>, freebsd-hackers@freebsd.org, freebsd-performance@freebsd.org Subject: Re: ACPI-fast default timecounter, but HPET 83% faster Message-ID: <7d6fde3d0904261927s1a67cf85jc982c1a68e30e081@mail.gmail.com> In-Reply-To: <200904270150.31912.pieter@degoeje.nl> References: <200904270150.31912.pieter@degoeje.nl>
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On Sun, Apr 26, 2009 at 4:50 PM, Pieter de Goeje <pieter@degoeje.nl> wrote:
> Dear hackers,
>
> While fiddling with the sysctl kern.timecounter.hardware, I found out tha=
t on
> my system HPET is significantly faster than ACPI-fast. Using the program
> below I measured the number of clock_gettime() calls the system can execu=
te
> per second. I ran the program 10 times for each configuration and here ar=
e
> the results:
>
> x ACPI-fast
> + HPET
> +------------------------------------------------------------------------=
-+
> |x =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 +|
> |x =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 +|
> |x =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0++|
> |x =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0++|
> |x =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0++|
> |x =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0++|
> |A =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|A|
> +------------------------------------------------------------------------=
-+
> =A0 =A0N =A0 =A0 =A0 =A0 =A0 Min =A0 =A0 =A0 =A0 =A0 Max =A0 =A0 =A0 =A0M=
edian =A0 =A0 =A0 =A0 =A0 Avg =A0 =A0 =A0 =A0Stddev
> x =A010 =A0 =A0 =A0 =A0822032 =A0 =A0 =A0 =A0823752 =A0 =A0 =A0 =A0823551=
=A0 =A0 =A0823397.8 =A0 =A0 509.43254
> + =A010 =A0 =A0 =A0 1498348 =A0 =A0 =A0 1506862 =A0 =A0 =A0 1502830 =A0 =
=A0 1503267.4 =A0 =A0 2842.9779
> Difference at 95.0% confidence
> =A0 =A0 =A0 =A0679870 +/- 1918.94
> =A0 =A0 =A0 =A082.5688% +/- 0.233052%
> =A0 =A0 =A0 =A0(Student's t, pooled s =3D 2042.31)
>
> System details: Intel(R) Core(TM)2 Duo CPU E6750 =A0@ 2.66GHz (3200.02-MH=
z
> 686-class CPU), Gigabyte P35-DS3R motherboard running i386 -CURRENT updat=
ed
> today.
>
> Unfortunately I only have one system with a HPET timecounter, so I cannot
> verify these results on another system. If similar results are obtained o=
n
> other machines, I think the HPET timecounter quality needs to be increase=
d
> beyond that of ACPI-fast.
>
> Regards,
>
> Pieter de Goeje
>
> ----- 8< ----- clock_gettime.c ----- 8< ------
> #include <sys/time.h>
> #include <stdio.h>
> #include <time.h>
>
> #define COUNT 1000000
>
> int main() {
> =A0 =A0 =A0 =A0struct timespec ts_start, ts_stop, ts_read;
> =A0 =A0 =A0 =A0double time;
> =A0 =A0 =A0 =A0int i;
>
> =A0 =A0 =A0 =A0clock_gettime(CLOCK_MONOTONIC, &ts_start);
> =A0 =A0 =A0 =A0for(i =3D 0; i < COUNT; i++) {
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0clock_gettime(CLOCK_MONOTONIC, &ts_read);
> =A0 =A0 =A0 =A0}
> =A0 =A0 =A0 =A0clock_gettime(CLOCK_MONOTONIC, &ts_stop);
>
> =A0 =A0 =A0 =A0time =3D (ts_stop.tv_sec - ts_start.tv_sec) + (ts_stop.tv_=
nsec -
> ts_start.tv_nsec) * 1E-9;
> =A0 =A0 =A0 =A0printf("%.0f\n", COUNT / time);
> }
I'm seeing similar results.
[root@orangebox /usr/home/gcooper]# dmesg | grep 'Timecounter "'
Timecounter "i8254" frequency 1193182 Hz quality 0
Timecounter "ACPI-fast" frequency 3579545 Hz quality 1000
Timecounter "HPET" frequency 14318180 Hz quality 900
[root@orangebox /usr/home/gcooper]# ./cgt
1369355
[root@orangebox /usr/home/gcooper]# sysctl
kern.timecounter.hardware=3D"ACPI-fast"
kern.timecounter.hardware: HPET -> ACPI-fast
[root@orangebox /usr/home/gcooper]# ./cgt
772289
Why's the default ACPI-fast? For power-saving functionality or because
of the `quality' factor? What is the criteria that determines the
`quality' of a clock as what's being reported above (I know what
determines the quality of a clock visually from a oscilloscope =3D])?
Thanks,
-Garrett
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