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Date: Sat, 19 Sep 2009 18:50:13 +0100 From: Daniel J Blueman <daniel.blueman@...il.com> To: Arjan van de Ven <arjan@...radead.org> Cc: Linux Kernel <linux-kernel@...r.kernel.org> Subject: Re: tickless and HZ=1000 throughput advantage? On Sat, Sep 19, 2009 at 3:55 PM, Arjan van de Ven <arjan@...radead.org> wrote: > On Sat, 19 Sep 2009 15:47:24 +0100 > Daniel J Blueman <daniel.blueman@...il.com> wrote: > >> On tickless kernels, is the general consensus that for non-embedded >> systems, selecting HZ=1000 gives slightly more throughput in >> particular situations than HZ=100 or 250, due to finer timer >> intervals/granularity? > > it's not about throughput. It's about latency for some things.... > although now that select/poll and co use hrtimers it's not as critical > anymore. > > the HZ timers aren't used much for anything time-critical nowadays. Agreed. Do you think there is still a small case for moving to HZ=1000 (given it's effectively free) in situations like: jiffies_to_transmit = port->baud?(1 + charsleft * 10 * HZ / port->baud):0; <applying plausible figures> (gdb) p (1 + 10 * 10 * 1000 / 38400) * 1 $3 = 3 (gdb) p (1 + 10 * 10 * 250 / 38400) * 4 $5 = 4 -> HZ=250 causes a 33% longer sleep than expected perhaps? -- Daniel J Blueman -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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