Hello all! Running rack @b7b78c1c169 "Optimize HPTS..." very happy on my laptop (amd64)!
Thanks all! Drew Gallatin <galla...@freebsd.org> escreveu (quinta, 21/03/2024 à(s) 12:58): > The entire point is to *NOT* go through the overhead of scheduling > something asynchronously, but to take advantage of the fact that a > user/kernel transition is going to trash the cache anyway. > > In the common case of a system which has less than the threshold number > of connections , we access the tcp_hpts_softclock function pointer, make > one function call, and access hpts_that_need_softclock, and then return. > So that's 2 variables and a function call. > > I think it would be preferable to avoid that call, and to move the > declaration of tcp_hpts_softclock and hpts_that_need_softclock so that they > are in the same cacheline. Then we'd be hitting just a single line in the > common case. (I've made comments on the review to that effect). > > Also, I wonder if the threshold could get higher by default, so that hpts > is never called in this context unless we're to the point where we're > scheduling thousands of runs of the hpts thread (and taking all those clock > interrupts). > > Drew > > On Wed, Mar 20, 2024, at 8:17 PM, Konstantin Belousov wrote: > > On Tue, Mar 19, 2024 at 06:19:52AM -0400, rrs wrote: > > Ok I have created > > > > https://reviews.freebsd.org/D44420 > > > > > > To address the issue. I also attach a short version of the patch that > Nuno > > can try and validate > > > > it works. Drew you may want to try this and validate the optimization > does > > kick in since I can > > > > only now test that it does not on my local box :) > The patch still causes access to all cpu's cachelines on each userret. > It would be much better to inc/check the threshold and only schedule the > call when exceeded. Then the call can occur in some dedicated context, > like per-CPU thread, instead of userret. > > > > > > > R > > > > > > > > On 3/18/24 3:42 PM, Drew Gallatin wrote: > > > No. The goal is to run on every return to userspace for every thread. > > > > > > Drew > > > > > > On Mon, Mar 18, 2024, at 3:41 PM, Konstantin Belousov wrote: > > > > 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) > > > > > > > > > > > > > > > > > > > > > > > diff --git a/sys/netinet/tcp_hpts.c b/sys/netinet/tcp_hpts.c > > index 8c4d2d41a3eb..eadbee19f69c 100644 > > --- a/sys/netinet/tcp_hpts.c > > +++ b/sys/netinet/tcp_hpts.c > > @@ -216,6 +216,7 @@ struct tcp_hpts_entry { > > void *ie_cookie; > > uint16_t p_num; /* The hpts number one per cpu */ > > uint16_t p_cpu; /* The hpts CPU */ > > + uint8_t hit_callout_thresh; > > /* There is extra space in here */ > > /* Cache line 0x100 */ > > struct callout co __aligned(CACHE_LINE_SIZE); > > @@ -269,6 +270,11 @@ static struct hpts_domain_info { > > int cpu[MAXCPU]; > > } hpts_domains[MAXMEMDOM]; > > > > +counter_u64_t hpts_that_need_softclock; > > +SYSCTL_COUNTER_U64(_net_inet_tcp_hpts_stats, OID_AUTO, needsoftclock, > CTLFLAG_RD, > > + &hpts_that_need_softclock, > > + "Number of hpts threads that need softclock"); > > + > > counter_u64_t hpts_hopelessly_behind; > > > > SYSCTL_COUNTER_U64(_net_inet_tcp_hpts_stats, OID_AUTO, hopeless, > CTLFLAG_RD, > > @@ -334,7 +340,7 @@ SYSCTL_INT(_net_inet_tcp_hpts, OID_AUTO, precision, > CTLFLAG_RW, > > &tcp_hpts_precision, 120, > > "Value for PRE() precision of callout"); > > SYSCTL_INT(_net_inet_tcp_hpts, OID_AUTO, cnt_thresh, CTLFLAG_RW, > > - &conn_cnt_thresh, 0, > > + &conn_cnt_thresh, DEFAULT_CONNECTION_THESHOLD, > > "How many connections (below) make us use the callout based > mechanism"); > > SYSCTL_INT(_net_inet_tcp_hpts, OID_AUTO, logging, CTLFLAG_RW, > > &hpts_does_tp_logging, 0, > > @@ -1548,6 +1554,9 @@ __tcp_run_hpts(void) > > struct tcp_hpts_entry *hpts; > > int ticks_ran; > > > > + if (counter_u64_fetch(hpts_that_need_softclock) == 0) > > + return; > > + > > hpts = tcp_choose_hpts_to_run(); > > > > if (hpts->p_hpts_active) { > > @@ -1683,6 +1692,13 @@ tcp_hpts_thread(void *ctx) > > ticks_ran = tcp_hptsi(hpts, 1); > > tv.tv_sec = 0; > > tv.tv_usec = hpts->p_hpts_sleep_time * HPTS_TICKS_PER_SLOT; > > + if ((hpts->p_on_queue_cnt > conn_cnt_thresh) && > (hpts->hit_callout_thresh == 0)) { > > + hpts->hit_callout_thresh = 1; > > + counter_u64_add(hpts_that_need_softclock, 1); > > + } else if ((hpts->p_on_queue_cnt <= conn_cnt_thresh) && > (hpts->hit_callout_thresh == 1)) { > > + hpts->hit_callout_thresh = 0; > > + counter_u64_add(hpts_that_need_softclock, -1); > > + } > > if (hpts->p_on_queue_cnt >= conn_cnt_thresh) { > > if(hpts->p_direct_wake == 0) { > > /* > > @@ -1818,6 +1834,7 @@ tcp_hpts_mod_load(void) > > cpu_top = NULL; > > #endif > > tcp_pace.rp_num_hptss = ncpus; > > + hpts_that_need_softclock = counter_u64_alloc(M_WAITOK); > > hpts_hopelessly_behind = counter_u64_alloc(M_WAITOK); > > hpts_loops = counter_u64_alloc(M_WAITOK); > > back_tosleep = counter_u64_alloc(M_WAITOK); > > @@ -2042,6 +2059,7 @@ tcp_hpts_mod_unload(void) > > free(tcp_pace.grps, M_TCPHPTS); > > #endif > > > > + counter_u64_free(hpts_that_need_softclock); > > counter_u64_free(hpts_hopelessly_behind); > > counter_u64_free(hpts_loops); > > counter_u64_free(back_tosleep); > > > > -- Nuno Teixeira FreeBSD Committer (ports)
