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Message-Id: <1340594a-4eef-424c-9bc3-fbc16224ba77@app.fastmail.com>
Date: Tue, 08 Jul 2025 22:42:27 +0100
From: "Jiaxun Yang" <jiaxun.yang@...goat.com>
To: "Gregory CLEMENT" <gregory.clement@...tlin.com>,
"Thomas Bogendoerfer" <tsbogend@...ha.franken.de>
Cc: "Vladimir Kondratiev" <vladimir.kondratiev@...ileye.com>,
Théo Lebrun <theo.lebrun@...tlin.com>,
"Tawfik Bayouk" <tawfik.bayouk@...ileye.com>,
"Thomas Petazzoni" <thomas.petazzoni@...tlin.com>,
"linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] MIPS: CPS: Improve mips_cps_first_online_in_cluster()
在2025年7月8日周二 下午2:46，Gregory CLEMENT写道：
> The initial implementation of this function goes through all the CPUs
> in a cluster to determine if the current CPU is the only one
> running. This process occurs every time the function is called.
>
> However, during boot, we already perform this task, so let's take
> advantage of this opportunity to create and fill a CPU bitmask that
> can be easily and efficiently used later.
>
> This patch modifies the function to allow providing the first
> available online CPU when one already exists, which is necessary for
> delay CPU calibration optimization.
>
> Signed-off-by: Gregory CLEMENT <gregory.clement@...tlin.com>
Reviewed-by: Jiaxun Yang <jiaxun.yang@...goat.com>
Many thanks for this optimised implementation!
Thanks
- Jiaxun
> ---
> arch/mips/include/asm/mips-cps.h | 4 +++-
> arch/mips/include/asm/smp-cps.h | 1 +
> arch/mips/kernel/mips-cm.c | 47 ++++++++++++++--------------------------
> arch/mips/kernel/smp-cps.c | 5 ++++-
> 4 files changed, 24 insertions(+), 33 deletions(-)
>
> diff --git a/arch/mips/include/asm/mips-cps.h
> b/arch/mips/include/asm/mips-cps.h
> index
> 917009b80e6951dc7e2b308ad7fb42cd9fbbf7d7..1fffd47a4564fb891d3c1e3ae3895b34d6700e5e
> 100644
> --- a/arch/mips/include/asm/mips-cps.h
> +++ b/arch/mips/include/asm/mips-cps.h
> @@ -258,6 +258,8 @@ static inline bool mips_cps_multicluster_cpus(void)
>
> /**
> * mips_cps_first_online_in_cluster() - Detect if CPU is first online
> in cluster
> + * @first_cpu: The first other online CPU in cluster, or nr_cpu_ids if
> + * the function returns true.
> *
> * Determine whether the local CPU is the first to be brought online
> in its
> * cluster - that is, whether there are any other online CPUs in the
> local
> @@ -265,6 +267,6 @@ static inline bool mips_cps_multicluster_cpus(void)
> *
> * Returns true if this CPU is first online, else false.
> */
> -extern unsigned int mips_cps_first_online_in_cluster(void);
> +extern unsigned int mips_cps_first_online_in_cluster(int *first_cpu);
>
> #endif /* __MIPS_ASM_MIPS_CPS_H__ */
> diff --git a/arch/mips/include/asm/smp-cps.h
> b/arch/mips/include/asm/smp-cps.h
> index
> 10d3ebd890cb2f3ac2b1db5a541cfe9e7f1a0c99..88cfae5d22c83e44451200ad3daae12fced03303
> 100644
> --- a/arch/mips/include/asm/smp-cps.h
> +++ b/arch/mips/include/asm/smp-cps.h
> @@ -24,6 +24,7 @@ struct core_boot_config {
>
> struct cluster_boot_config {
> unsigned long *core_power;
> + struct cpumask cpumask;
> struct core_boot_config *core_config;
> };
>
> diff --git a/arch/mips/kernel/mips-cm.c b/arch/mips/kernel/mips-cm.c
> index
> 43cb1e20baed3648ff83bb5d3bbe6a726072e063..f49138f551d3c347c6a98afe05ad5027b0d91637
> 100644
> --- a/arch/mips/kernel/mips-cm.c
> +++ b/arch/mips/kernel/mips-cm.c
> @@ -10,6 +10,7 @@
> #include <linux/spinlock.h>
>
> #include <asm/mips-cps.h>
> +#include <asm/smp-cps.h>
> #include <asm/mipsregs.h>
>
> void __iomem *mips_gcr_base;
> @@ -529,39 +530,23 @@ void mips_cm_error_report(void)
> write_gcr_error_cause(cm_error);
> }
>
> -unsigned int mips_cps_first_online_in_cluster(void)
> +unsigned int mips_cps_first_online_in_cluster(int *first_cpu)
> {
> - unsigned int local_cl;
> - int i;
> -
> - local_cl = cpu_cluster(¤t_cpu_data);
> + unsigned int local_cl = cpu_cluster(¤t_cpu_data);
> + struct cpumask *local_cl_mask;
>
> /*
> - * We rely upon knowledge that CPUs are numbered sequentially by
> - * cluster - ie. CPUs 0..X will be in cluster 0, CPUs X+1..Y in
> cluster
> - * 1, CPUs Y+1..Z in cluster 2 etc. This means that CPUs in the same
> - * cluster will immediately precede or follow one another.
> - *
> - * First we scan backwards, until we find an online CPU in the cluster
> - * or we move on to another cluster.
> + * mips_cps_cluster_bootcfg is allocated in cps_prepare_cpus. If it is
> + * not yet done, then we are so early that only one CPU is running, so
> + * it is the first online CPU in the cluster.
> */
> - for (i = smp_processor_id() - 1; i >= 0; i--) {
> - if (cpu_cluster(&cpu_data[i]) != local_cl)
> - break;
> - if (!cpu_online(i))
> - continue;
> - return false;
> - }
> -
> - /* Then do the same for higher numbered CPUs */
> - for (i = smp_processor_id() + 1; i < nr_cpu_ids; i++) {
> - if (cpu_cluster(&cpu_data[i]) != local_cl)
> - break;
> - if (!cpu_online(i))
> - continue;
> - return false;
> - }
> -
> - /* We found no online CPUs in the local cluster */
> - return true;
> + if (mips_cps_cluster_bootcfg)
> + local_cl_mask = &mips_cps_cluster_bootcfg[local_cl].cpumask;
> + else
> + return true;
> +
> + *first_cpu = cpumask_any_and_but(local_cl_mask,
> + cpu_online_mask,
> + smp_processor_id());
> + return (*first_cpu >= nr_cpu_ids);
> }
> diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
> index
> 7b0e69af4097025196b93115139a5e89c1d71fcc..6c5f15293a8e58a701601b242f43ba19a6814f06
> 100644
> --- a/arch/mips/kernel/smp-cps.c
> +++ b/arch/mips/kernel/smp-cps.c
> @@ -283,7 +283,7 @@ static void __init cps_smp_setup(void)
>
> static void __init cps_prepare_cpus(unsigned int max_cpus)
> {
> - unsigned int nclusters, ncores, core_vpes, c, cl, cca;
> + unsigned int nclusters, ncores, core_vpes, nvpe = 0, c, cl, cca;
> bool cca_unsuitable, cores_limited;
> struct cluster_boot_config *cluster_bootcfg;
> struct core_boot_config *core_bootcfg;
> @@ -356,10 +356,13 @@ static void __init cps_prepare_cpus(unsigned int max_cpus)
>
> /* Allocate VPE boot configuration structs */
> for (c = 0; c < ncores; c++) {
> + int v;
> core_vpes = core_vpe_count(cl, c);
> core_bootcfg[c].vpe_config = kcalloc(core_vpes,
> sizeof(*core_bootcfg[c].vpe_config),
> GFP_KERNEL);
> + for (v = 0; v < core_vpes; v++)
> + cpumask_set_cpu(nvpe++, &mips_cps_cluster_bootcfg[cl].cpumask);
> if (!core_bootcfg[c].vpe_config)
> goto err_out;
> }
>
> --
> 2.47.2
--
- Jiaxun
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