diff mbox series

[v3,net,1/3] rcu: add a helper to report consolidated flavor QS

Message ID f71214e6221c5c50b32a62a33697473c756e604e.1710346410.git.yan@cloudflare.com (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series Report RCU QS for busy network kthreads | expand

Checks

Context Check Description
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for net
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag present in non-next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 15258 this patch: 15258
netdev/build_tools success Errors and warnings before: 0 this patch: 0
netdev/cc_maintainers warning 7 maintainers not CCed: jiangshanlai@gmail.com frederic@kernel.org josh@joshtriplett.org mathieu.desnoyers@efficios.com boqun.feng@gmail.com quic_neeraju@quicinc.com qiang.zhang1211@gmail.com
netdev/build_clang success Errors and warnings before: 3081 this patch: 3081
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 16175 this patch: 16175
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 29 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc fail Errors and warnings before: 0 this patch: 1
netdev/source_inline success Was 0 now: 0
netdev/contest success net-next-2024-03-14--12-00 (tests: 908)

Commit Message

Yan Zhai March 13, 2024, 4:25 p.m. UTC 
There are several scenario in network processing that can run
extensively under heavy traffic. In such situation, RCU synchronization
might not observe desired quiescent states for indefinitely long period.
Create a helper to safely raise the desired RCU quiescent states for
such scenario.

Reviewed-by: Jesper Dangaard Brouer <hawk@kernel.org>
Signed-off-by: Yan Zhai <yan@cloudflare.com>
---
 include/linux/rcupdate.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

Comments

Jakub Kicinski March 14, 2024, 9:54 p.m. UTC | #1 
On Wed, 13 Mar 2024 09:25:49 -0700 Yan Zhai wrote:
> +/**
> + * rcu_softirq_qs_periodic - Periodically report consolidated quiescent states

> +#define rcu_softirq_qs_periodic(old_ts) \

scripts/kernel-doc says:

include/linux/rcupdate.h:271: warning: Function parameter or struct member 'old_ts' not described in 'rcu_softirq_qs_periodic'
Yan Zhai March 15, 2024, 2:54 p.m. UTC | #2 
On Thu, Mar 14, 2024 at 4:55 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Wed, 13 Mar 2024 09:25:49 -0700 Yan Zhai wrote:
> > +/**
> > + * rcu_softirq_qs_periodic - Periodically report consolidated quiescent states
>
> > +#define rcu_softirq_qs_periodic(old_ts) \
>
> scripts/kernel-doc says:
>
TIL, thanks. Let me send v4 to amend the text.

Yan

> include/linux/rcupdate.h:271: warning: Function parameter or struct member 'old_ts' not described in 'rcu_softirq_qs_periodic'
> --
> pw-bot: cr
diff mbox series

Patch

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 0746b1b0b663..e91ae38c33e3 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -247,6 +247,29 @@  do { \
 	cond_resched(); \
 } while (0)
 
+/**
+ * rcu_softirq_qs_periodic - Periodically report consolidated quiescent states
+ *
+ * This helper is for network processing in non-RT kernels, where there could
+ * be busy polling threads that block RCU synchronization indefinitely.  In
+ * such context, simply calling cond_resched is insufficient, so give it a
+ * stronger push to eliminate potential blockage of all RCU types.
+ *
+ * NOTE: unless absolutely sure, this helper should in general be called
+ * outside of bh lock section to avoid reporting a surprising QS to updaters,
+ * who could be expecting RCU read critical section to end at local_bh_enable().
+ */
+#define rcu_softirq_qs_periodic(old_ts) \
+do { \
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT) && \
+	    time_after(jiffies, (old_ts) + HZ / 10)) { \
+		preempt_disable(); \
+		rcu_softirq_qs(); \
+		preempt_enable(); \
+		(old_ts) = jiffies; \
+	} \
+} while (0)
+
 /*
  * Infrastructure to implement the synchronize_() primitives in
  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.