On Mon, Mar 18, 2024 at 03:13:11PM -0400, Drew Gallatin wrote: > I got the idea from > https://people.mpi-sws.org/~druschel/publications/soft-timers-tocs.pdf > The gist is that the TCP pacing stuff needs to run frequently, and > rather than run it out of a clock interrupt, its more efficient to run > it out of a system call context at just the point where we return to > userspace and the cache is trashed anyway. The current implementation > is fine for our workload, but probably not idea for a generic system. > Especially one where something is banging on system calls. > > Ast's could be the right tool for this, but I'm super unfamiliar with > them, and I can't find any docs on them. > > Would ast_register(0, ASTR_UNCOND, 0, func) be roughly equivalent to > what's happening here? This call would need some AST number added, and then it registers the ast to run on next return to userspace, for the current thread.
Is it enough? > > Drew > > On Mon, Mar 18, 2024, at 2:33 PM, Konstantin Belousov wrote: > > On Mon, Mar 18, 2024 at 07:26:10AM -0500, Mike Karels wrote: > > > On 18 Mar 2024, at 7:04, tue...@freebsd.org wrote: > > > > > > >> On 18. Mar 2024, at 12:42, Nuno Teixeira <edua...@freebsd.org> wrote: > > > >> > > > >> Hello all! > > > >> > > > >> It works just fine! > > > >> System performance is OK. > > > >> Using patch on main-n268841-b0aaf8beb126(-dirty). > > > >> > > > >> --- > > > >> net.inet.tcp.functions_available: > > > >> Stack D Alias PCB > > > >> count > > > >> freebsd freebsd 0 > > > >> rack * rack 38 > > > >> --- > > > >> > > > >> It would be so nice that we can have a sysctl tunnable for this patch > > > >> so we could do more tests without recompiling kernel. > > > > Thanks for testing! > > > > > > > > @gallatin: can you come up with a patch that is acceptable for Netflix > > > > and allows to mitigate the performance regression. > > > > > > Ideally, tcphpts could enable this automatically when it starts to be > > > used (enough?), but a sysctl could select auto/on/off. > > There is already a well-known mechanism to request execution of the > > specific function on return to userspace, namely AST. The difference > > with the current hack is that the execution is requested for one callback > > in the context of the specific thread. > > > > Still, it might be worth a try to use it; what is the reason to hit a thread > > that does not do networking, with TCP processing? > > > > > > > > Mike > > > > > > > Best regards > > > > Michael > > > >> > > > >> Thanks all! > > > >> Really happy here :) > > > >> > > > >> Cheers, > > > >> > > > >> Nuno Teixeira <edua...@freebsd.org> escreveu (domingo, 17/03/2024 à(s) > > > >> 20:26): > > > >>> > > > >>> Hello, > > > >>> > > > >>>> 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? > > > >>>> > > > >>>> 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: > > > >>> > > > >>> It's affecting overall system performance, bonnie was just a way to > > > >>> get some numbers to compare. > > > >>> > > > >>> Tomorrow I will test patch. > > > >>> > > > >>> Thanks! > > > >>> > > > >>> -- > > > >>> Nuno Teixeira > > > >>> FreeBSD Committer (ports) > > > >> > > > >> > > > >> > > > >> -- > > > >> Nuno Teixeira > > > >> FreeBSD Committer (ports) > > > > >
