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McKenney" , Linus Torvalds , Anna-Maria Behnsen , Eric Dumazet Subject: [RFC PATCH 0/6] softirq: Start pushing down the big softirq lock Date: Tue, 1 Aug 2023 15:24:35 +0200 Message-Id: <20230801132441.559222-1-frederic@kernel.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Spam-Status: No, score=-7.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1773036109862943258 X-GMAIL-MSGID: 1773036109862943258 Networking softirqs can take time, holding the execution of block, tasklets, timers and RCU callbacks. People fight hard through this big softirq lock, proposing more and more hacks over the years to deal with the resulting fundamental unfairness that is not only a problem for RT users. Here is a proposal for an entrypoint to dealing with that issue in the long term. The purpose is to adopt a similar journey to the one we took with the BKL push-down but with timers. Most timers are unrelated to other softirq vectors, those can simply be tagged with the new TIMER_SOFTINTERRUPTIBLE flag that makes a callback soft-interruptible. The others can carry the TIMER_SOFTINTERRUPTIBLE after they get converted to use appropriate synchronization against other vectors callbacks (using spin_lock_bh() for example). Once all timers are dealt with after a few years (famous last words), they can be handled separately from the softirq infrastructure. RCU could follow a similar treatment, if we manage to find room for a flag somewhere... (Only -RT and x86 are supported for now) git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git timers/softirq-preemptible HEAD: c233aee141ddb78d07b2f7311be38cfc286de654 Thanks, Frederic --- Frederic Weisbecker (6): softirq: Turn set_softirq_pending() to reset_softirq_pending() softirq: Make softirq handling entry/exit generally available softirq: Introduce softirq disabled mask x86/softirq: Support softirq disabled mask timers: Introduce soft-interruptible timers timers: Make process_timeout() soft-interruptible arch/Kconfig | 3 +++ arch/x86/Kconfig | 1 + arch/x86/include/asm/current.h | 1 + arch/x86/include/asm/hardirq.h | 1 + include/linux/bottom_half.h | 9 +++++++++ include/linux/interrupt.h | 15 ++++++++++++--- include/linux/timer.h | 5 +++-- kernel/softirq.c | 40 ++++++++++++++++++++++++++++++++-------- kernel/time/timer.c | 20 +++++++++++++++++++- 9 files changed, 81 insertions(+), 14 deletions(-)