> On 28. Mar 2024, at 15:00, Nuno Teixeira <edua...@freebsd.org> wrote: > > Hello all! > > Running rack @b7b78c1c169 "Optimize HPTS..." very happy on my laptop (amd64)! > > Thanks all! Thanks for the feedback!
Best regards Michael > > 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)
