Re: [PATCH] RISC-V: Probe misaligned access speed in parallel
From: Jisheng Zhang
Date: Wed Nov 01 2023 - 07:44:10 EST
On Sat, Sep 16, 2023 at 04:39:54PM +0800, Jisheng Zhang wrote:
> On Fri, Sep 15, 2023 at 11:49:03AM -0700, Evan Green wrote:
> > Probing for misaligned access speed takes about 0.06 seconds. On a
> > system with 64 cores, doing this in smp_callin() means it's done
> > serially, extending boot time by 3.8 seconds. That's a lot of boot time.
> >
> > Instead of measuring each CPU serially, let's do the measurements on
> > all CPUs in parallel. If we disable preemption on all CPUs, the
> > jiffies stop ticking, so we can do this in stages of 1) everybody
> > except core 0, then 2) core 0.
> >
> > The measurement call in smp_callin() stays around, but is now
> > conditionalized to only run if a new CPU shows up after the round of
> > in-parallel measurements has run. The goal is to have the measurement
> > call not run during boot or suspend/resume, but only on a hotplug
> > addition.
> >
> > Signed-off-by: Evan Green <evan@xxxxxxxxxxxx>
>
> Reported-by: Jisheng Zhang <jszhang@xxxxxxxxxx>
Hi Evan, Palmer,
This patch seems missing in v6.6, I dunno what happened.
And this patch doesn't fix the boot time regression but also fix a real
bug during cpu hotplug on and off.
Here is the reproduce script:
while true
do
echo 0 > /sys/devices/system/cpu/cpu1/online
echo 1 > /sys/devices/system/cpu/cpu1/online
done
Here is the BUG log on qemu:
[ 20.950753] CPU1: failed to come online
[ 20.951875] ------------[ cut here ]------------
[ 20.952070] kernel BUG at kernel/time/hrtimer.c:2227!
[ 20.952341] Kernel BUG [#1]
[ 20.952366] Modules linked in:
[ 20.952515] CPU: 0 PID: 46 Comm: sh Not tainted 6.6.0 #3
[ 20.952607] Hardware name: riscv-virtio,qemu (DT)
[ 20.952695] epc : hrtimers_dead_cpu+0x22e/0x230
[ 20.952808] ra : cpuhp_invoke_callback+0xe4/0x54e
[ 20.952844] epc : ffffffff8007d6c0 ra : ffffffff8000f904 sp : ff600000011ebb30
[ 20.952863] gp : ffffffff80d081d0 tp : ff6000000134da00 t0 : 0000000000000040
[ 20.952880] t1 : 0000000000000000 t2 : 0000000000000000 s0 : ff600000011ebbb0
[ 20.952895] s1 : 0000000000000001 a0 : 0000000000000001 a1 : 000000000000002c
[ 20.952911] a2 : 0000000000000000 a3 : 0000000000000000 a4 : 0000000000000000
[ 20.952926] a5 : 0000000000000001 a6 : 0000000000000538 a7 : 0000000000000000
[ 20.952941] s2 : 000000000000002c s3 : 0000000000000000 s4 : ff6000003ffd4390
[ 20.952957] s5 : ffffffff80d0a1f8 s6 : 0000000000000000 s7 : ffffffff8007d492
[ 20.952972] s8 : 0000000000000001 s9 : fffffffffffffffb s10: 0000000000000000
[ 20.952987] s11: 00005555820dc708 t3 : 0000000000000002 t4 : 0000000000000402
[ 20.953002] t5 : ff600000010f0710 t6 : ff600000010f0718
[ 20.953016] status: 0000000200000120 badaddr: 0000000000000000 cause: 0000000000000003
[ 20.953124] [<ffffffff8007d6c0>] hrtimers_dead_cpu+0x22e/0x230
[ 20.953226] [<ffffffff8000f904>] cpuhp_invoke_callback+0xe4/0x54e
[ 20.953241] [<ffffffff80010fb8>] _cpu_up+0x200/0x2a2
[ 20.953254] [<ffffffff800110ac>] cpu_up+0x52/0x8a
[ 20.953266] [<ffffffff80011654>] cpu_device_up+0x14/0x1c
[ 20.953279] [<ffffffff8029abb6>] cpu_subsys_online+0x1e/0x68
[ 20.953296] [<ffffffff802957de>] device_online+0x3c/0x70
[ 20.953306] [<ffffffff8029587a>] online_store+0x68/0x8c
[ 20.953317] [<ffffffff802909ba>] dev_attr_store+0xe/0x1a
[ 20.953330] [<ffffffff801df8aa>] sysfs_kf_write+0x2a/0x34
[ 20.953346] [<ffffffff801def06>] kernfs_fop_write_iter+0xde/0x162
[ 20.953360] [<ffffffff8018154a>] vfs_write+0x136/0x320
[ 20.953372] [<ffffffff801818e4>] ksys_write+0x4a/0xb4
[ 20.953383] [<ffffffff80181962>] __riscv_sys_write+0x14/0x1c
[ 20.953394] [<ffffffff803dec7e>] do_trap_ecall_u+0x4a/0x110
[ 20.953420] [<ffffffff80003666>] ret_from_exception+0x0/0x66
[ 20.953648] Code: 7c42 7ca2 7d02 6de2 4501 6109 8082 c0ef 7463 bd1d (9002) 1141
[ 20.953897] ---[ end trace 0000000000000000 ]---
[ 20.954068] Kernel panic - not syncing: Fatal exception in interrupt
[ 20.954128] SMP: stopping secondary CPUs
[ 22.749953] SMP: failed to stop secondary CPUs 0-1
[ 22.803768] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---
> >
> > ---
> >
> > Jisheng, I didn't add your Tested-by tag since the patch evolved from
> > the one you tested. Hopefully this one brings you the same result.
> >
> > ---
> > arch/riscv/include/asm/cpufeature.h | 3 ++-
> > arch/riscv/kernel/cpufeature.c | 28 +++++++++++++++++++++++-----
> > arch/riscv/kernel/smpboot.c | 11 ++++++++++-
> > 3 files changed, 35 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> > index d0345bd659c9..19e7817eba10 100644
> > --- a/arch/riscv/include/asm/cpufeature.h
> > +++ b/arch/riscv/include/asm/cpufeature.h
> > @@ -30,6 +30,7 @@ DECLARE_PER_CPU(long, misaligned_access_speed);
> > /* Per-cpu ISA extensions. */
> > extern struct riscv_isainfo hart_isa[NR_CPUS];
> >
> > -void check_unaligned_access(int cpu);
> > +extern bool misaligned_speed_measured;
> > +int check_unaligned_access(void *unused);
> >
> > #endif
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index 1cfbba65d11a..8eb36e1dfb95 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -42,6 +42,9 @@ struct riscv_isainfo hart_isa[NR_CPUS];
> > /* Performance information */
> > DEFINE_PER_CPU(long, misaligned_access_speed);
> >
> > +/* Boot-time in-parallel unaligned access measurement has occurred. */
> > +bool misaligned_speed_measured;
>
> This var can be avoided, see below.
>
> > +
> > /**
> > * riscv_isa_extension_base() - Get base extension word
> > *
> > @@ -556,8 +559,9 @@ unsigned long riscv_get_elf_hwcap(void)
> > return hwcap;
> > }
> >
> > -void check_unaligned_access(int cpu)
> > +int check_unaligned_access(void *unused)
> > {
> > + int cpu = smp_processor_id();
> > u64 start_cycles, end_cycles;
> > u64 word_cycles;
> > u64 byte_cycles;
> > @@ -571,7 +575,7 @@ void check_unaligned_access(int cpu)
> > page = alloc_pages(GFP_NOWAIT, get_order(MISALIGNED_BUFFER_SIZE));
> > if (!page) {
> > pr_warn("Can't alloc pages to measure memcpy performance");
> > - return;
> > + return 0;
> > }
> >
> > /* Make an unaligned destination buffer. */
> > @@ -643,15 +647,29 @@ void check_unaligned_access(int cpu)
> >
> > out:
> > __free_pages(page, get_order(MISALIGNED_BUFFER_SIZE));
> > + return 0;
> > +}
> > +
> > +static void check_unaligned_access_nonboot_cpu(void *param)
> > +{
> > + if (smp_processor_id() != 0)
> > + check_unaligned_access(param);
> > }
> >
> > -static int check_unaligned_access_boot_cpu(void)
> > +static int check_unaligned_access_all_cpus(void)
> > {
> > - check_unaligned_access(0);
> > + /* Check everybody except 0, who stays behind to tend jiffies. */
> > + on_each_cpu(check_unaligned_access_nonboot_cpu, NULL, 1);
> > +
> > + /* Check core 0. */
> > + smp_call_on_cpu(0, check_unaligned_access, NULL, true);
> > +
> > + /* Boot-time measurements are complete. */
> > + misaligned_speed_measured = true;
> > return 0;
> > }
> >
> > -arch_initcall(check_unaligned_access_boot_cpu);
> > +arch_initcall(check_unaligned_access_all_cpus);
> >
> > #ifdef CONFIG_RISCV_ALTERNATIVE
> > /*
> > diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> > index 1b8da4e40a4d..39322ae20a75 100644
> > --- a/arch/riscv/kernel/smpboot.c
> > +++ b/arch/riscv/kernel/smpboot.c
> > @@ -27,6 +27,7 @@
> > #include <linux/sched/mm.h>
> > #include <asm/cpu_ops.h>
> > #include <asm/cpufeature.h>
> > +#include <asm/hwprobe.h>
> > #include <asm/irq.h>
> > #include <asm/mmu_context.h>
> > #include <asm/numa.h>
> > @@ -246,7 +247,15 @@ asmlinkage __visible void smp_callin(void)
> >
> > numa_add_cpu(curr_cpuid);
> > set_cpu_online(curr_cpuid, 1);
> > - check_unaligned_access(curr_cpuid);
> > +
> > + /*
> > + * Boot-time misaligned access speed measurements are done in parallel
> > + * in an initcall. Only measure here for hotplug.
> > + */
> > + if (misaligned_speed_measured &&
> > + (per_cpu(misaligned_access_speed, curr_cpuid) == RISCV_HWPROBE_MISALIGNED_UNKNOWN)) {
>
> I believe this check is for cpu not-booted during boot time but hotplug in
> after that, if so I'm not sure whether
> misaligned_speed_measured can be replaced with
> (system_state == SYSTEM_RUNNING)
> then we don't need misaligned_speed_measured at all.
>
> > + check_unaligned_access(NULL);
> > + }
> >
> > if (has_vector()) {
> > if (riscv_v_setup_vsize())
> > --
> > 2.34.1
> >