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From:   Anup Patel <anup@brainfault.org>
Date:   Sat, 23 Nov 2019 09:55:54 +0530
Message-ID: <CAAhSdy1j0z09tytn0dFVBc7AAVo3EZEJwXRKUFJ9RWbok77bMg@mail.gmail.com>
Subject: Re: [PATCH 2/2] riscv: defconfigs: enable more debugging options
To:     Paul Walmsley <paul.walmsley@sifive.com>
Cc:     linux-riscv <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>
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On Sat, Nov 23, 2019 at 4:28 AM Paul Walmsley <paul.walmsley@sifive.com> wrote:
>
> Enable more debugging options in the RISC-V defconfigs to help kernel
> developers catch problems with patches earlier in the development
> cycle.

Lot the debug options enabled by this patch have big performance
impact. I would suggest to have separate debug defconfig for
RV32 and RV64 with debug options enabled instead of enabling
these in regular defconfigs.

>
> Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
> ---
>  arch/riscv/configs/defconfig      | 23 +++++++++++++++++++++++
>  arch/riscv/configs/rv32_defconfig | 23 +++++++++++++++++++++++
>  2 files changed, 46 insertions(+)
>
> diff --git a/arch/riscv/configs/defconfig b/arch/riscv/configs/defconfig
> index f0710d8f50cc..e2ff95cb3390 100644
> --- a/arch/riscv/configs/defconfig
> +++ b/arch/riscv/configs/defconfig
> @@ -101,4 +101,27 @@ CONFIG_CRYPTO_USER_API_HASH=y
>  CONFIG_CRYPTO_DEV_VIRTIO=y
>  CONFIG_PRINTK_TIME=y
>  CONFIG_DEBUG_FS=y
> +CONFIG_DEBUG_PAGEALLOC=y
> +CONFIG_DEBUG_VM=y
> +CONFIG_DEBUG_VM_PGFLAGS=y
> +CONFIG_DEBUG_MEMORY_INIT=y
> +CONFIG_DEBUG_PER_CPU_MAPS=y

> +CONFIG_SOFTLOCKUP_DETECTOR=y

This one is fine.

> +CONFIG_WQ_WATCHDOG=y

Is WQ_WATCHDOG as debug option ?

> +CONFIG_SCHED_STACK_END_CHECK=y
> +CONFIG_DEBUG_TIMEKEEPING=y
> +CONFIG_DEBUG_RT_MUTEXES=y
> +CONFIG_DEBUG_SPINLOCK=y
> +CONFIG_DEBUG_MUTEXES=y
> +CONFIG_DEBUG_RWSEMS=y
> +CONFIG_DEBUG_ATOMIC_SLEEP=y
> +CONFIG_STACKTRACE=y
> +CONFIG_DEBUG_LIST=y
> +CONFIG_DEBUG_PLIST=y
> +CONFIG_DEBUG_SG=y

All these debug options reduce kernel performance
in a noticeable way. Please have separate defconfig
for these options.

>  # CONFIG_RCU_TRACE is not set
> +CONFIG_RCU_EQS_DEBUG=y
> +CONFIG_DEBUG_BLOCK_EXT_DEVT=y
> +# CONFIG_FTRACE is not set
> +# CONFIG_RUNTIME_TESTING_MENU is not set
> +CONFIG_MEMTEST=y
> diff --git a/arch/riscv/configs/rv32_defconfig b/arch/riscv/configs/rv32_defconfig
> index bdec58e6c5f7..eb519407c841 100644
> --- a/arch/riscv/configs/rv32_defconfig
> +++ b/arch/riscv/configs/rv32_defconfig
> @@ -98,4 +98,27 @@ CONFIG_CRYPTO_USER_API_HASH=y
>  CONFIG_CRYPTO_DEV_VIRTIO=y
>  CONFIG_PRINTK_TIME=y
>  CONFIG_DEBUG_FS=y
> +CONFIG_DEBUG_PAGEALLOC=y
> +CONFIG_DEBUG_VM=y
> +CONFIG_DEBUG_VM_PGFLAGS=y
> +CONFIG_DEBUG_MEMORY_INIT=y
> +CONFIG_DEBUG_PER_CPU_MAPS=y
> +CONFIG_SOFTLOCKUP_DETECTOR=y
> +CONFIG_WQ_WATCHDOG=y
> +CONFIG_SCHED_STACK_END_CHECK=y
> +CONFIG_DEBUG_TIMEKEEPING=y
> +CONFIG_DEBUG_RT_MUTEXES=y
> +CONFIG_DEBUG_SPINLOCK=y
> +CONFIG_DEBUG_MUTEXES=y
> +CONFIG_DEBUG_RWSEMS=y
> +CONFIG_DEBUG_ATOMIC_SLEEP=y
> +CONFIG_STACKTRACE=y
> +CONFIG_DEBUG_LIST=y
> +CONFIG_DEBUG_PLIST=y
> +CONFIG_DEBUG_SG=y
>  # CONFIG_RCU_TRACE is not set
> +CONFIG_RCU_EQS_DEBUG=y
> +CONFIG_DEBUG_BLOCK_EXT_DEVT=y
> +# CONFIG_FTRACE is not set
> +# CONFIG_RUNTIME_TESTING_MENU is not set
> +CONFIG_MEMTEST=y

Same comments as above.

> --
> 2.24.0.rc0
>

The debug and trace instrumentation although helpful
in development comes with performance overhead. We
should be careful in enabling debug and trace options
by default in defconfigs.

Regards,
Anup