epoch(9) background information?

[Sebastian Huber]

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.

-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber at embedded-brains.de
PGP     : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.