​Perhaps the mail didn't arrive properly, but the fq performance is okay
now. I don't know why it was completely out for a couple of tests. It was
most likely my mistake or some very bad timing for testing.

I see that on my physical hosts tsc is also the default with hpet in the
list of available clocksources, just as in the VM (where kvm-clock is a
paravirtualized version of the host tsc) so the same behaviour is probably
to be expected in the VM as on the physical hosts. As far as I know I have
not seen that it is a requirement to actually run:

echo hpet > /sys/devices/system/clocksource/clocksource0/current_clocksource

... before using fq as most (physical) linux hosts use tsc as the default
clock source today unless the kernel detects unreliabilities.
​

On 25 January 2017 at 22:48, Eric Dumazet <eric.dumazet@gmail.com> wrote:

> I do not know any particular issues with FQ in VM
>
> If you have a recent tc binary (iproute2 package) you can get some
> infos, as mentioned in this commit changelog :
>
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/
> linux.git/commit/?id=fefa569a9d4bc4b7758c0fddd75bb0382c95da77
>
>
> $ tc -s qd sh dev eth0 | grep latency
> 0 gc, 0 highprio, 32490767 throttled, 2382 ns latency
>
>
> On Wed, 2017-01-25 at 22:31 +0100, Hans-Kristian Bakke wrote:
> > kvm-clock is a paravirtualized clock that seems to use the CPUs TSC
> > capabilities if they exist. But it may not be perfect:
> >
> >
> > https://access.redhat.com/documentation/en-US/Red_Hat_
> Enterprise_Linux/6/html/Virtualization_Host_Configuration_and_Guest_
> Installation_Guide/chap-Virtualization_Host_Configuration_and_Guest_
> Installation_Guide-KVM_guest_timing_management.html
> >
> >
> > On 25 January 2017 at 22:29, Hans-Kristian Bakke <hkbakke@gmail.com>
> > wrote:
> >         Actually I think that is because it may be using the newer
> >         TSC:
> >          dmesg | grep clocksource
> >         [    0.000000] clocksource: kvm-clock: mask:
> >         0xffffffffffffffff max_cycles: 0x1cd42e4dffb, max_idle_ns:
> >         881590591483 ns
> >         [    0.000000] clocksource: refined-jiffies: mask: 0xffffffff
> >         max_cycles: 0xffffffff, max_idle_ns: 7645519600211568 ns
> >         [    0.000000] clocksource: hpet: mask: 0xffffffff max_cycles:
> >         0xffffffff, max_idle_ns: 19112604467 ns
> >         [    0.092665] clocksource: jiffies: mask: 0xffffffff
> >         max_cycles: 0xffffffff, max_idle_ns: 7645041785100000 ns
> >         [    0.366429] clocksource: Switched to clocksource kvm-clock
> >         [    0.378974] clocksource: acpi_pm: mask: 0xffffff
> >         max_cycles: 0xffffff, max_idle_ns: 2085701024 ns
> >         [    1.666474] tsc: Refined TSC clocksource calibration:
> >         3200.013 MHz
> >         [    1.666479] clocksource: tsc: mask: 0xffffffffffffffff
> >         max_cycles: 0x2e20562a1bb, max_idle_ns: 440795285529 ns
> >
> >
> >
> >         On 25 January 2017 at 22:26, Jonathan Morton
> >         <chromatix99@gmail.com> wrote:
> >
> >                 > On 25 Jan, 2017, at 23:20, Hans-Kristian Bakke
> >                 <hkbakke@gmail.com> wrote:
> >                 >
> >                 > ​[    0.000000] ACPI: HPET 0x00000000BFFE274F 000038
> >                 (v01 BOCHS  BXPCHPET 00000001 BXPC 00000001)
> >                 > [    0.000000] ACPI: HPET id: 0x8086a201 base:
> >                 0xfed00000
> >                 > [    0.000000] clocksource: hpet: mask: 0xffffffff
> >                 max_cycles: 0xffffffff, max_idle_ns: 19112604467 ns
> >                 > [    0.000000] hpet clockevent registered
> >                 > [    0.362335] hpet0: at MMIO 0xfed00000, IRQs 2, 8,
> >                 0
> >                 > [    0.362339] hpet0: 3 comparators, 64-bit
> >                 100.000000 MHz counter
> >                 > [    0.661731] rtc_cmos 00:00: alarms up to one day,
> >                 y3k, 114 bytes nvram, hpet irqs
> >
> >                 Conspicuously absent here is a line saying
> >                 “clocksource: Switched to clocksource hpet”.  That may
> >                 be worth examining in more detail.
> >
> >                  - Jonathan Morton
> >
> >
> >
> >
> >
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>
>
>