<div dir="ltr">Reminder from years back: we would love to have a Haifux talk about timers, time, tickless kernel, Jiffies, etc.<div>So if you (that's you) are reading this, and are interested in the topic, what is a better time to learn it to depth and talk about it?</div>
<div><br></div><div>Thanks</div><div>Orna<br><br><div class="gmail_quote">On Wed, Jul 25, 2012 at 3:28 PM, Oleg Goldshmidt <span dir="ltr"><<a href="mailto:pub@goldshmidt.org" target="_blank">pub@goldshmidt.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><font face="georgia,serif"><br></font><br><div class="gmail_quote"><div class="im">On Wed, Jul 25, <a href="tel:2012" value="+9722012" target="_blank">2012</a> at 2:29 PM, Nadav Har'El <span dir="ltr"><<a href="mailto:nyh@math.technion.ac.il" target="_blank">nyh@math.technion.ac.il</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br>
HZ used to default to 100 in the Linux kernel, but now it actually<br>
defaults (unless I'm mis-remembering) to 250, and this is where the 4-ms<br>
resolution came from. </blockquote></div><div><br>Actually, there is the default HZ and inside the kernel HZ there is HZ that you can configure at compile time (with CONFIG_HZ) and USER_HZ, which, I think, is still 100 whether or not the kernel's HZ is customized. I think USER_HZ is what is important for "soft timers" you are interested in.<br>
<br>Unless you configure the kernel yourself, the HZ value the kernel comes with probably depends on the distro. The tradeoff is as follows: desktop systems benefit from a higher HZ value because interactive processes are latency-sensitive. Servers, especially NUMA systems, don't have interactive processes and may, on the other hand, experience a lot of unpleasant effects (bus contention as an example) if there are lots of interrupts. Also note that the interrupt rate will be HZ*#CPUs.<br>
<br>I am used to RedHat systems whose kernels normally come with HZ=100. You are talking about a server as well, right? You may be right about HZ=250 by default in the vanilla kernel that is supposed to be a compromise between 100 and 1000.<br>
<br>If you go back to, say, <a href="tel:2.6.11" value="+9722611" target="_blank">2.6.11</a> or <a href="tel:2.6.12" value="+9722612" target="_blank">2.6.12</a>, then you'll see HZ=1000 by default, I think. Was that "Linux on a desktop"? ;-)<span class="HOEnZb"><font color="#888888"><br>
</font></span></div><span class="HOEnZb"><font color="#888888"><br></font></span></div><span class="HOEnZb"><font color="#888888">-- <br>Oleg Goldshmidt | <a href="mailto:oleg@goldshmidt.org" target="_blank">oleg@goldshmidt.org</a><br>
</font></span></div>
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<br></blockquote></div><br><br clear="all"><div><br></div>-- <br>Orna Agmon Ben-Yehuda.<br><a href="http://ladypine.org">http://ladypine.org</a><br>
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