Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism

[Bart Van Assche]

On 9/4/19 11:02 AM, Peter Zijlstra wrote:
> On Wed, Sep 04, 2019 at 10:38:59AM -0700, Bart Van Assche wrote:
> > I think it is widely known that rdtsc is a relatively slow x86 instruction.
> > So I expect that using that instruction will cause a measurable overhead if
> > it is called frequently enough. I'm not aware of any publicly available
> > measurement data however.
>
> https://www.agner.org/optimize/instruction_tables.pdf
>
> RDTSC, Ryzen: ~36
> RDTSC, Skylake: ~20
>
> Sadly those same tables don't list the cost of actual exceptions or even
> IRET :/

Thanks Peter for having looked up these numbers. These numbers are much 
better than last time I checked. Ming, would CONFIG_IRQ_TIME_ACCOUNTING 
help your workload?

Does anyone know which CPUs the following text from 
Documentation/admin-guide/kernel-parameters.txt refers to?

tsc=		[ ... ]
		[x86] noirqtime: Do not use TSC to do irq accounting.
		Used to run time disable IRQ_TIME_ACCOUNTING on any
		platforms where RDTSC is slow and this accounting
		can add overhead.

Bart.