Re: [Bloat] Initial tests with BBR in kernel 4.9

[Hans-Kristian Bakke <hkbakke@gmail.com>]

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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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