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Date: Tue, 9 Jan 2024 19:22:38 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Souradeep Chakrabarti <schakrabarti@...ux.microsoft.com>,
"kys@...rosoft.com" <kys@...rosoft.com>, "haiyangz@...rosoft.com"
<haiyangz@...rosoft.com>, "wei.liu@...nel.org" <wei.liu@...nel.org>,
"decui@...rosoft.com" <decui@...rosoft.com>, "davem@...emloft.net"
<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
"longli@...rosoft.com" <longli@...rosoft.com>, "yury.norov@...il.com"
<yury.norov@...il.com>, "leon@...nel.org" <leon@...nel.org>,
"cai.huoqing@...ux.dev" <cai.huoqing@...ux.dev>,
"ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>,
"vkuznets@...hat.com" <vkuznets@...hat.com>, "tglx@...utronix.de"
<tglx@...utronix.de>, "linux-hyperv@...r.kernel.org"
<linux-hyperv@...r.kernel.org>, "netdev@...r.kernel.org"
<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "linux-rdma@...r.kernel.org"
<linux-rdma@...r.kernel.org>
CC: "schakrabarti@...rosoft.com" <schakrabarti@...rosoft.com>,
"paulros@...rosoft.com" <paulros@...rosoft.com>
Subject: RE: [PATCH 3/4 net-next] net: mana: add a function to spread IRQs per
CPUs
From: Souradeep Chakrabarti <schakrabarti@...ux.microsoft.com> Sent: Tuesday, January 9, 2024 2:51 AM
>
> From: Yury Norov <yury.norov@...il.com>
>
> Souradeep investigated that the driver performs faster if IRQs are
> spread on CPUs with the following heuristics:
>
> 1. No more than one IRQ per CPU, if possible;
> 2. NUMA locality is the second priority;
> 3. Sibling dislocality is the last priority.
>
> Let's consider this topology:
>
> Node 0 1
> Core 0 1 2 3
> CPU 0 1 2 3 4 5 6 7
>
> The most performant IRQ distribution based on the above topology
> and heuristics may look like this:
>
> IRQ Nodes Cores CPUs
> 0 1 0 0-1
> 1 1 1 2-3
> 2 1 0 0-1
> 3 1 1 2-3
> 4 2 2 4-5
> 5 2 3 6-7
> 6 2 2 4-5
> 7 2 3 6-7
I didn't pay attention to the detailed discussion of this issue
over the past 2 to 3 weeks during the holidays in the U.S., but
the above doesn't align with the original problem as I understood
it. I thought the original problem was to avoid putting IRQs on
both hyper-threads in the same core, and that the perf
improvements are based on that configuration. At least that's
what the commit message for Patch 4/4 in this series says.
The above chart results in 8 IRQs being assigned to the 8 CPUs,
probably with 1 IRQ per CPU. At least on x86, if the affinity
mask for an IRQ contains multiple CPUs, matrix_find_best_cpu()
should balance the IRQ assignments between the CPUs in the mask.
So the original problem is still present because both hyper-threads
in a core are likely to have an IRQ assigned.
Of course, this example has 8 IRQs and 8 CPUs, so assigning an
IRQ to every hyper-thread may be the only choice. If that's the
case, maybe this just isn't a good example to illustrate the
original problem and solution. But even with a better example
where the # of IRQs is <= half the # of CPUs in a NUMA node,
I don't think the code below accomplishes the original intent.
Maybe I've missed something along the way in getting to this
version of the patch. Please feel free to set me straight. :-)
Michael
>
> The irq_setup() routine introduced in this patch leverages the
> for_each_numa_hop_mask() iterator and assigns IRQs to sibling groups
> as described above.
>
> According to [1], for NUMA-aware but sibling-ignorant IRQ distribution
> based on cpumask_local_spread() performance test results look like this:
>
> /ntttcp -r -m 16
> NTTTCP for Linux 1.4.0
> ---------------------------------------------------------
> 08:05:20 INFO: 17 threads created
> 08:05:28 INFO: Network activity progressing...
> 08:06:28 INFO: Test run completed.
> 08:06:28 INFO: Test cycle finished.
> 08:06:28 INFO: ##### Totals: #####
> 08:06:28 INFO: test duration :60.00 seconds
> 08:06:28 INFO: total bytes :630292053310
> 08:06:28 INFO: throughput :84.04Gbps
> 08:06:28 INFO: retrans segs :4
> 08:06:28 INFO: cpu cores :192
> 08:06:28 INFO: cpu speed :3799.725MHz
> 08:06:28 INFO: user :0.05%
> 08:06:28 INFO: system :1.60%
> 08:06:28 INFO: idle :96.41%
> 08:06:28 INFO: iowait :0.00%
> 08:06:28 INFO: softirq :1.94%
> 08:06:28 INFO: cycles/byte :2.50
> 08:06:28 INFO: cpu busy (all) :534.41%
>
> For NUMA- and sibling-aware IRQ distribution, the same test works
> 15% faster:
>
> /ntttcp -r -m 16
> NTTTCP for Linux 1.4.0
> ---------------------------------------------------------
> 08:08:51 INFO: 17 threads created
> 08:08:56 INFO: Network activity progressing...
> 08:09:56 INFO: Test run completed.
> 08:09:56 INFO: Test cycle finished.
> 08:09:56 INFO: ##### Totals: #####
> 08:09:56 INFO: test duration :60.00 seconds
> 08:09:56 INFO: total bytes :741966608384
> 08:09:56 INFO: throughput :98.93Gbps
> 08:09:56 INFO: retrans segs :6
> 08:09:56 INFO: cpu cores :192
> 08:09:56 INFO: cpu speed :3799.791MHz
> 08:09:56 INFO: user :0.06%
> 08:09:56 INFO: system :1.81%
> 08:09:56 INFO: idle :96.18%
> 08:09:56 INFO: iowait :0.00%
> 08:09:56 INFO: softirq :1.95%
> 08:09:56 INFO: cycles/byte :2.25
> 08:09:56 INFO: cpu busy (all) :569.22%
>
> [1]
> https://lore.kernel.org/all/20231211063726.GA4977@linuxonhyperv3.guj3
> yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net/
>
> Signed-off-by: Yury Norov <yury.norov@...il.com>
> Co-developed-by: Souradeep Chakrabarti
> <schakrabarti@...ux.microsoft.com>
> ---
> .../net/ethernet/microsoft/mana/gdma_main.c | 29
> +++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
> diff --git a/drivers/net/ethernet/microsoft/mana/gdma_main.c
> b/drivers/net/ethernet/microsoft/mana/gdma_main.c
> index 6367de0c2c2e..6a967d6be01e 100644
> --- a/drivers/net/ethernet/microsoft/mana/gdma_main.c
> +++ b/drivers/net/ethernet/microsoft/mana/gdma_main.c
> @@ -1243,6 +1243,35 @@ void mana_gd_free_res_map(struct gdma_resource *r)
> r->size = 0;
> }
>
> +static __maybe_unused int irq_setup(unsigned int *irqs, unsigned int len, int node)
> +{
> + const struct cpumask *next, *prev = cpu_none_mask;
> + cpumask_var_t cpus __free(free_cpumask_var);
> + int cpu, weight;
> +
> + if (!alloc_cpumask_var(&cpus, GFP_KERNEL))
> + return -ENOMEM;
> +
> + rcu_read_lock();
> + for_each_numa_hop_mask(next, node) {
> + weight = cpumask_weight_andnot(next, prev);
> + while (weight > 0) {
> + cpumask_andnot(cpus, next, prev);
> + for_each_cpu(cpu, cpus) {
> + if (len-- == 0)
> + goto done;
> + irq_set_affinity_and_hint(*irqs++, topology_sibling_cpumask(cpu));
> + cpumask_andnot(cpus, cpus, topology_sibling_cpumask(cpu));
> + --weight;
> + }
> + }
> + prev = next;
> + }
> +done:
> + rcu_read_unlock();
> + return 0;
> +}
> +
> static int mana_gd_setup_irqs(struct pci_dev *pdev)
> {
> unsigned int max_queues_per_port = num_online_cpus();
> --
> 2.34.1
>
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