From: Yury Norov <ynorov@caviumnetworks.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Chris Metcalf <cmetcalf@mellanox.com>,
Christopher Lameter <cl@linux.com>,
Russell King - ARM Linux <linux@armlinux.org.uk>,
Mark Rutland <mark.rutland@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>
Cc: Yury Norov <ynorov@caviumnetworks.com>,
linux-arm-kernel@lists.infradead.org,
linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: [PATCH 0/2] smp: don't kick CPUs running idle or nohz_full tasks
Date: Sun, 25 Mar 2018 20:50:02 +0300 [thread overview]
Message-ID: <20180325175004.28162-1-ynorov@caviumnetworks.com> (raw)
kick_all_cpus_sync() is used to broadcast IPIs to all online CPUs to force
them sync caches, TLB etc. It is is called only 3 times - from mm/slab,
arm64 and powerpc code.
With framework introduced in patch b8c17e6664c46 ("rcu: Maintain special
bits at bottom of ->dynticks counter") we can delay synchrosization work
for CPUs in extended quiescent state (idle or nohz_full userspace).
As Paul E. McKenney wrote:
--
Currently, IPIs are used to force other CPUs to invalidate their TLBs
in response to a kernel virtual-memory mapping change. This works, but
degrades both battery lifetime (for idle CPUs) and real-time response
(for nohz_full CPUs), and in addition results in unnecessary IPIs due to
the fact that CPUs executing in usermode are unaffected by stale kernel
mappings. It would be better to cause a CPU executing in usermode to
wait until it is entering kernel mode to do the flush, first to avoid
interrupting usemode tasks and second to handle multiple flush requests
with a single flush in the case of a long-running user task.
--
For mm/slab and arm64 it looks safe to delay synchronization. This is done
in patch #2 by introducing kick_active_cpus_sync() function. For powerpc -
I'm not sure, and I'd like to ask powerpc people, is it safe to do same
also for that code? If so, we can completely drop kick_all_cpus_sync().
Yury Norov (2):
rcu: declare rcu_eqs_special_set() in public header
smp: introduce kick_active_cpus_sync()
arch/arm64/kernel/insn.c | 2 +-
include/linux/rcutree.h | 1 +
include/linux/smp.h | 2 ++
kernel/smp.c | 24 ++++++++++++++++++++++++
mm/slab.c | 2 +-
5 files changed, 29 insertions(+), 2 deletions(-)
--
2.14.1
next reply other threads:[~2018-03-25 17:50 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-25 17:50 Yury Norov [this message]
2018-03-25 17:50 ` [PATCH 1/2] rcu: declare rcu_eqs_special_set() in public header Yury Norov
2018-03-25 19:12 ` Paul E. McKenney
2018-03-25 19:18 ` Yury Norov
2018-03-25 17:50 ` [PATCH 2/2] smp: introduce kick_active_cpus_sync() Yury Norov
2018-03-25 19:23 ` Paul E. McKenney
2018-03-25 20:11 ` Yury Norov
2018-03-26 12:45 ` Paul E. McKenney
2018-03-28 13:36 ` Yury Norov
2018-03-28 13:56 ` Paul E. McKenney
2018-03-28 14:41 ` Yury Norov
2018-03-28 14:45 ` Paul E. McKenney
2018-03-26 8:53 ` Andrea Parri
2018-03-26 18:57 ` Steven Rostedt
2018-03-28 12:59 ` Yury Norov
2018-03-27 10:21 ` Will Deacon
2018-03-28 10:58 ` Yury Norov
2018-04-01 11:11 ` Yury Norov
2018-04-01 14:10 ` Paul E. McKenney
2018-04-03 13:48 ` Mark Rutland
2018-04-04 3:36 ` Yury Norov
2018-04-04 9:08 ` Mark Rutland
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180325175004.28162-1-ynorov@caviumnetworks.com \
--to=ynorov@caviumnetworks.com \
--cc=akpm@linux-foundation.org \
--cc=benh@kernel.crashing.org \
--cc=catalin.marinas@arm.com \
--cc=cl@linux.com \
--cc=cmetcalf@mellanox.com \
--cc=iamjoonsoo.kim@lge.com \
--cc=kvm-ppc@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux@armlinux.org.uk \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mark.rutland@arm.com \
--cc=mathieu.desnoyers@efficios.com \
--cc=mpe@ellerman.id.au \
--cc=paulmck@linux.vnet.ibm.com \
--cc=paulus@samba.org \
--cc=penberg@kernel.org \
--cc=rientjes@google.com \
--cc=rostedt@goodmis.org \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).