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Donenfeld" To: gregkh@linuxfoundation.org, stable@vger.kernel.org Cc: "Jason A. Donenfeld" Subject: [PATCH stable 4.9.y 4.14.y] random: use expired timer rather than wq for mixing fast pool Date: Thu, 13 Oct 2022 11:07:31 -0600 Message-Id: <20221013170731.1456197-1-Jason@zx2c4.com> In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org commit 748bc4dd9e663f23448d8ad7e58c011a67ea1eca upstream. Previously, the fast pool was dumped into the main pool periodically in the fast pool's hard IRQ handler. This worked fine and there weren't problems with it, until RT came around. Since RT converts spinlocks into sleeping locks, problems cropped up. Rather than switching to raw spinlocks, the RT developers preferred we make the transformation from originally doing: do_some_stuff() spin_lock() do_some_other_stuff() spin_unlock() to doing: do_some_stuff() queue_work_on(some_other_stuff_worker) This is an ordinary pattern done all over the kernel. However, Sherry noticed a 10% performance regression in qperf TCP over a 40gbps InfiniBand card. Quoting her message: > MT27500 Family [ConnectX-3] cards: > Infiniband device 'mlx4_0' port 1 status: > default gid: fe80:0000:0000:0000:0010:e000:0178:9eb1 > base lid: 0x6 > sm lid: 0x1 > state: 4: ACTIVE > phys state: 5: LinkUp > rate: 40 Gb/sec (4X QDR) > link_layer: InfiniBand > > Cards are configured with IP addresses on private subnet for IPoIB > performance testing. > Regression identified in this bug is in TCP latency in this stack as reported > by qperf tcp_lat metric: > > We have one system listen as a qperf server: > [root@yourQperfServer ~]# qperf > > Have the other system connect to qperf server as a client (in this > case, it’s X7 server with Mellanox card): > [root@yourQperfClient ~]# numactl -m0 -N0 qperf 20.20.20.101 -v -uu -ub --time 60 --wait_server 20 -oo msg_size:4K:1024K:*2 tcp_lat Rather than incur the scheduling latency from queue_work_on, we can instead switch to running on the next timer tick, on the same core. This also batches things a bit more -- once per jiffy -- which is okay now that mix_interrupt_randomness() can credit multiple bits at once. Reported-by: Sherry Yang Tested-by: Paul Webb Cc: Sherry Yang Cc: Phillip Goerl Cc: Jack Vogel Cc: Nicky Veitch Cc: Colm Harrington Cc: Ramanan Govindarajan Cc: Sebastian Andrzej Siewior Cc: Dominik Brodowski Cc: Tejun Heo Cc: Sultan Alsawaf Cc: stable@vger.kernel.org Fixes: 58340f8e952b ("random: defer fast pool mixing to worker") Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index bf5f0149d9d4..174dd139d2f3 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -894,7 +894,7 @@ struct fast_pool { unsigned long pool[4]; unsigned long last; unsigned int count; - struct work_struct mix; + struct timer_list mix; }; static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = { @@ -946,9 +946,9 @@ int __cold random_online_cpu(unsigned int cpu) } #endif -static void mix_interrupt_randomness(struct work_struct *work) +static void mix_interrupt_randomness(unsigned long data) { - struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix); + struct fast_pool *fast_pool = (struct fast_pool *)data; /* * The size of the copied stack pool is explicitly 2 longs so that we * only ever ingest half of the siphash output each time, retaining @@ -1000,10 +1000,14 @@ void add_interrupt_randomness(int irq) if (new_count < 1024 && !time_is_before_jiffies(fast_pool->last + HZ)) return; - if (unlikely(!fast_pool->mix.func)) - INIT_WORK(&fast_pool->mix, mix_interrupt_randomness); + if (unlikely(!fast_pool->mix.data)) + setup_timer(&fast_pool->mix, mix_interrupt_randomness, (unsigned long)fast_pool); + fast_pool->count |= MIX_INFLIGHT; - queue_work_on(raw_smp_processor_id(), system_highpri_wq, &fast_pool->mix); + if (!timer_pending(&fast_pool->mix)) { + fast_pool->mix.expires = jiffies; + add_timer_on(&fast_pool->mix, raw_smp_processor_id()); + } } EXPORT_SYMBOL_GPL(add_interrupt_randomness); -- 2.37.3