Commit Graph

5 Commits

Author SHA1 Message Date
Gleb Smirnoff
49fef6a202 Create two public UMA_ZONE_PCPU zones: 64 bit sized and pointer sized.
Sponsored by:	Nginx, Inc.
2014-02-10 19:59:46 +00:00
Gleb Smirnoff
e28a647db6 Revert r249590 and in case if mp_ncpus isn't initialized use MAXCPU. This
allows us to init counter zone at early stage of boot.

Reviewed by:	kib
Tested by:	Lytochkin Boris <lytboris gmail.com>
2013-07-23 11:16:40 +00:00
Konstantin Belousov
70a7dd5d5b Fix issues with zeroing and fetching the counters, on x86 and ppc64.
Issues were noted by Bruce Evans and are present on all architectures.

On i386, a counter fetch should use atomic read of 64bit value,
otherwise carry from the increment on other CPU could be lost for the
given fetch, making error of 2^32.  If 64bit read (cmpxchg8b) is not
available on the machine, it cannot be SMP and it is enough to disable
preemption around read to avoid the split read.

On x86 the counter increment is not atomic on purpose, which makes it
possible for the store of the incremented result to override just
zeroed per-cpu slot.  The effect would be a counter going off by
arbitrary value after zeroing.  Perform the counter zeroing on the
same processor which does the increments, making the operations
mutually exclusive.  On i386, same as for the fetching, if the
cmpxchg8b is not available, machine is not SMP and we disable
preemption for zeroing.

PowerPC64 is treated the same as amd64.

For other architectures, the changes made to allow the compilation to
succeed, without fixing the issues with zeroing or fetching.  It
should be possible to handle them by using the 64bit loads and stores
atomic WRT preemption (assuming the architectures also converted from
using critical sections to proper asm).  If architecture does not
provide the facility, using global (spin) mutex would be non-optimal
but working solution.

Noted by:  bde
Sponsored by:	The FreeBSD Foundation
2013-07-01 02:48:27 +00:00
Gleb Smirnoff
8f779cc541 On non-ACPI i386 mp_ncpus is initialized at SI_SUB_CPU, and this
prevents us from creating UMA_ZONE_PCPU zones earlier.

As bandaid shift initialization of counter(9) zone later.

Reviewed by:		kib
Reported & tested by:	Lytochkin Boris <lytboris gmail.com>
2013-04-17 18:43:33 +00:00
Gleb Smirnoff
4e76af6a41 Merge from projects/counters: counter(9).
Introduce counter(9) API, that implements fast and raceless counters,
provided (but not limited to) for gathering of statistical data.

See http://lists.freebsd.org/pipermail/freebsd-arch/2013-April/014204.html
for more details.

In collaboration with:	kib
Reviewed by:		luigi
Tested by:		ae, ray
Sponsored by:		Nginx, Inc.
2013-04-08 19:40:53 +00:00