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> On 17. Mar 2024, at 16:39, Drew Gallatin <[email protected]> wrote:
>
> I don't have the full context, but it seems like the complaint is a performance regression in bonnie++ and perhaps other things when tcp_hpts is loaded, even when it is not used. Is that correct?
Correct.
>
> If so, I suspect its because we drive the tcp_hpts_softclock() routine from userret(), in order to avoid tons of timer interrupts and context switches. To test this theory, you could apply a patch like:
>
> diff --git a/sys/kern/subr_trap.c b/sys/kern/subr_trap.c
> index e9a16cd0b36e..54b540c97123 100644
> --- a/sys/kern/subr_trap.c
> +++ b/sys/kern/subr_trap.c
> @@ -138,7 +138,7 @@ userret(struct thread *td, struct trapframe *frame)
> * Software Timer Support for Network Processing"
> * by Mohit Aron and Peter Druschel.
> */
> - tcp_hpts_softclock();
> + /*tcp_hpts_softclock();*/
> /*
> * Let the scheduler adjust our priority etc.
> */
>
>
> If that fixes it, I suspect we should either make this hook optional for casual users of tcp_hpts(), or add some kind of "last called" timestamp to prevent it being called over and over and over on workloads which are syscall heavy.
Nuno, can you test that?
>
> Note that for non-casual users of hpts (like Netflix, with hundreds of thousands of TCP connections managed by hpts), this call is a huge win, so I think we'd prefer that it remain in some form.
Sure.
Best regards
Michael
>
> Drew