Date: Thu, 23 Aug 2018 12:27:12 +0200 From: Hans Petter Selasky <hps@selasky.org> To: Sebastian Huber <sebastian.huber@embedded-brains.de>, Eugene Grosbein <eugen@grosbein.net>, FreeBSD <freebsd-hackers@freebsd.org> Subject: Re: epoch(9) background information? Message-ID: <90e16238-6e4d-5d3d-499d-2a19a49be78c@selasky.org> In-Reply-To: <978ae736-89b9-6d83-e2a1-d2834ca8ae55@embedded-brains.de> References: <db397431-2c4c-64de-634a-20f38ce6a60e@embedded-brains.de> <3bfedcc3-0dae-7979-2bd4-da83f2c67e87@embedded-brains.de> <5B7E7804.4030907@grosbein.net> <978ae736-89b9-6d83-e2a1-d2834ca8ae55@embedded-brains.de>
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On 8/23/18 11:28 AM, Sebastian Huber wrote: > On 23/08/18 11:01, Eugene Grosbein wrote: >> On 23.08.2018 15:39, Sebastian Huber wrote: >> >>> We used the FreeBSD network stack also on low-end targets >>> (uni-processor) such as MCF548x ColdFire, Atmel SAM V71, SPARC LEON, >>> etc. in current production environments (not legacy systems). The >>> introduction of lock-free data structures (Concurrency Kit) and this >>> epoch memory reclamation makes little sense on these targets (at least >>> from my point of view). However, FreeBSD has still the SMP configuration >>> option (sys/conf/options) which suggests that SMP is optional. Is a >>> uni-processor system something which is considered by the FreeBSD >>> community as a thing worth supporting or can I expect that this is an >>> exotic environment which will get less and less well supported in the >>> future? I just need some guidance so that I can better plan for future >>> FreeBSD baseline updates. >> FreeBSD as virtualized uniprocessor guest should be supported at full >> scale, >> as well as embedded applications using single core x86 and non-x86 CPUs. > > If something should be supported, then there must be also someone who > ensures that this is actually the case. I don't know the FreeBSD > community good enough to judge if there is sufficient > manpower/funding/interest for a well supported uni-processor FreeBSD. > From the commits it is clear that FreeBSD receives a lot of attention > from CDN providers such as Netflix and Limelight Networks. They probably > don't care about uni-processor system support at all. The use of > lock-free data structures (Concurrency Kit) and the epoch memory > reclamation are now a mandatory infrastructure. There is no FreeBSD > configuration option to avoid this. > > The Concurrency Kit in sys/contrib/ck has no explicit support for the > FreeBSD RISC-V and MIPS architectures. So, I guess the fall-back > sys/contrib/ck/include/gcc/ck_pr.h is used. The atomic support in > sys/contrib/ck partially duplicates/extends the general atomic support > of the FreeBSD kernel ATOMIC(9). To me it is a bit unclear what will be > the future direction in the FreeBSD kernel with respect to lock-free > data structures. > Hi Sebastian, Do you have something like critical_enter() to disable pre-emption in your OS? If you don't need to support SMP, the CPU pinning in the EPOCH can be replaced by a critial_enter() / critial_exit() pair. --HPS
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