Date: Fri, 31 Oct 2008 11:04:04 +0200 From: Krassimir Slavchev <krassi@bulinfo.net> To: Julian Elischer <julian@elischer.org> Cc: freebsd-performance@freebsd.org, Sam Xia <xiazhongqi@huawei.com> Subject: Re: 1. thread switching time? (Krassimir Slavchev) Message-ID: <490ACA04.6060203@bulinfo.net> In-Reply-To: <490AB750.9040505@elischer.org> References: <000001c93b0c$6195e6b0$2f096f0a@china.huawei.com> <490AB477.2080001@bulinfo.net> <490AB750.9040505@elischer.org>
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Hello Julian,
Julian Elischer wrote:
> Krassimir Slavchev wrote:
>
>>
>> Also, I am able to set HZ=100000 but the thread switching time is still
>> ~1ms.
>
> You must be talking about the time that a thread can run before it is
> pushed out by other threads? I know I've seem many x 10,000 context
> switches in some cases, i.e. look at very high interrupt rates
> etc. so I guess I'm not sure what you are measuring..
Okay, I have a thread with:
while(1) {
clock_gettime(CLOCK_REALTIME, &tv);
nanosleep(&delay, NULL);
clock_gettime(CLOCK_REALTIME, &tv2);
timespecsub(&tv2, &tv);
}
If the delay is configured to be 0 < delay < 1ms I always get ~1ms delay.
Since nanosleep() is a cancellation point this means that the scheduler
will switch to another thread.
If the delay = 0 I get ~1600ns delay.
Yes. You are right. This is "the time that a thread can run before it is
pushed out by other threads".
Is there a way to decrease this time?
>
> at one time the scheduling quantum was independent of Hz.
> I am not sure how true that is now..
>
It seems to be independent of HZ.
Best Regards
>
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