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Introduce write-mostly sums

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wmsum counters are a reduced version of aggsum counters, optimized for
write-mostly scenarios.  They do not provide optimized read functions,
but instead allow much cheaper add function.  The primary usage is
infrequently read statistic counters, not requiring exact precision.

The Linux implementation is directly mapped into percpu_counter KPI.
The FreeBSD implementation is directly mapped into counter(9) KPI.
In user-space due to lack of better implementation mapped to aggsum.

Unfortunately neither Linux percpu_counter nor FreeBSD counter(9)
provide sufficient functionality to completelly replace aggsum, so
it still remains to be used for several hot counters.

Reviewed-by: Paul Dagnelie <pcd@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes #12114
This commit is contained in:
Alexander Motin
2021-05-27 16:27:29 -04:00
committed by Brian Behlendorf
parent 09c0a8fd1a
commit 85c43508f3
10 changed files with 319 additions and 72 deletions
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config/kernel-percpu.m4
+27
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@@ -25,6 +25,31 @@ AC_DEFUN([ZFS_AC_KERNEL_PERCPU_COUNTER_INIT], [
])
])
dnl #
dnl # 4.13 API change,
dnl # __percpu_counter_add() was renamed to percpu_counter_add_batch().
dnl #
AC_DEFUN([ZFS_AC_KERNEL_SRC_PERCPU_COUNTER_ADD_BATCH], [
ZFS_LINUX_TEST_SRC([percpu_counter_add_batch], [
#include <linux/percpu_counter.h>
],[
struct percpu_counter counter;
percpu_counter_add_batch(&counter, 1, 1);
])
])
AC_DEFUN([ZFS_AC_KERNEL_PERCPU_COUNTER_ADD_BATCH], [
AC_MSG_CHECKING([whether percpu_counter_add_batch() is defined])
ZFS_LINUX_TEST_RESULT([percpu_counter_add_batch], [
AC_MSG_RESULT(yes)
AC_DEFINE(HAVE_PERCPU_COUNTER_ADD_BATCH, 1,
[percpu_counter_add_batch() is defined])
],[
AC_MSG_RESULT(no)
])
])
dnl #
dnl # 5.10 API change,
dnl # The "count" was moved into ref->data, from ref
@@ -51,10 +76,12 @@ AC_DEFUN([ZFS_AC_KERNEL_PERCPU_REF_COUNT_IN_DATA], [
])
AC_DEFUN([ZFS_AC_KERNEL_SRC_PERCPU], [
ZFS_AC_KERNEL_SRC_PERCPU_COUNTER_INIT
ZFS_AC_KERNEL_SRC_PERCPU_COUNTER_ADD_BATCH
ZFS_AC_KERNEL_SRC_PERCPU_REF_COUNT_IN_DATA
])
AC_DEFUN([ZFS_AC_KERNEL_PERCPU], [
ZFS_AC_KERNEL_PERCPU_COUNTER_INIT
ZFS_AC_KERNEL_PERCPU_COUNTER_ADD_BATCH
ZFS_AC_KERNEL_PERCPU_REF_COUNT_IN_DATA
])