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From: "Arnd Bergmann" <arnd@arndb.de>
To: guoren <guoren@kernel.org>
Cc: "Palmer Dabbelt" <palmer@rivosinc.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Andy Lutomirski" <luto@kernel.org>,
	"Conor.Dooley" <conor.dooley@microchip.com>,
	"Heiko Stübner" <heiko@sntech.de>,
	"Jisheng Zhang" <jszhang@kernel.org>,
	lazyparser@gmail.com, falcon@tinylab.org,
	"Huacai Chen" <chenhuacai@kernel.org>,
	"Anup Patel" <apatel@ventanamicro.com>,
	"Atish Patra" <atishp@atishpatra.org>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
	Linux-Arch <linux-arch@vger.kernel.org>,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	"Guo Ren" <guoren@linux.alibaba.com>,
	"Andreas Schwab" <schwab@suse.de>
Subject: Re: [PATCH V4 8/8] riscv: Add config of thread stack size
Date: Sat, 10 Sep 2022 18:06:55 +0200	[thread overview]
Message-ID: <8817af55-de0d-4e8f-a41b-25d01d5fa968@www.fastmail.com> (raw)
In-Reply-To: <CAJF2gTQAMCjNyqrSOvqDAKR5Z-PZiTVxmoK9cvNAVQs+k2fZBg@mail.gmail.com>

On Sat, Sep 10, 2022, at 2:52 PM, Guo Ren wrote:
> On Thu, Sep 8, 2022 at 3:37 PM Arnd Bergmann <arnd@arndb.de> wrote:
>> On Thu, Sep 8, 2022, at 4:25 AM, guoren@kernel.org wrote:
>> > From: Guo Ren <guoren@linux.alibaba.com>
>> - When VMAP_STACK is set, make it possible to select non-power-of-two
>>   stack sizes. Most importantly, 12KB should be a really interesting
>>   choice as 8KB is probably still not enough for many 64-bit workloads,
>>   but 16KB is often more than what you need. You probably don't
>>   want to allow 64BIT/8KB without VMAP_STACK anyway since that just
>>   makes it really hard to debug, so hiding the option when VMAP_STACK
>>   is disabled may also be a good idea.
> I don't want this config to depend on VMAP_STACK. Some D1 chips would
> run with an 8K stack size and !VMAP_STACK.

That sounds like a really bad idea, why would you want to risk
using such a small stack without CONFIG_VMAP_STACK?

Are you worried about increased memory usage or something else?

>  /* thread information allocation */
> -#ifdef CONFIG_64BIT
> -#define THREAD_SIZE_ORDER      (2 + KASAN_STACK_ORDER)
> -#else
> -#define THREAD_SIZE_ORDER      (1 + KASAN_STACK_ORDER)
> -#endif
> +#define THREAD_SIZE_ORDER      CONFIG_THREAD_SIZE_ORDER
>  #define THREAD_SIZE            (PAGE_SIZE << THREAD_SIZE_ORDER)

This doesn't actually allow additional THREAD_SIZE values, as you
still round up to the nearest power of two.

I think all the non-arch code can deal with non-power-of-2
sizes, so you'd just need

#define THREAD_SIZE round_up(CONFIG_THREAD_SIZE, PAGE_SIZE)

and fix up the risc-v specific code to do the right thing
as well. I now see that THREAD_SIZE_ORDER is not actually
used anywhere with CONFIG_VMAP_STACK, so I suppose that
definition can be skipped, but you still need a THREAD_ALIGN
definition that is a power of two and at least a page larger
than THREAD_SIZE.

     Arnd

  reply	other threads:[~2022-09-10 16:07 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-08  2:24 [PATCH V4 0/9] riscv: Add GENERIC_ENTRY, irq stack support guoren
2022-09-08  2:24 ` [PATCH V4 1/8] riscv: elf_kexec: Fixup compile warning guoren
2022-09-08  2:25 ` [PATCH V4 2/8] riscv: compat_syscall_table: " guoren
2022-09-08  2:25 ` [PATCH V4 3/8] riscv: ptrace: Remove duplicate operation guoren
2022-09-08  2:25 ` [PATCH V4 4/8] riscv: traps: Add noinstr to prevent instrumentation inserted guoren
2022-09-08  7:33   ` Peter Zijlstra
2022-09-10  9:17     ` Guo Ren
2022-09-10 12:46       ` Guo Ren
2022-09-11 15:09       ` Peter Zijlstra
2022-09-11 16:20         ` Guo Ren
2022-09-08  2:25 ` [PATCH V4 5/8] riscv: convert to generic entry guoren
2022-09-15 13:50   ` Yipeng Zou
2022-09-08  2:25 ` [PATCH V4 6/8] riscv: Support HAVE_IRQ_EXIT_ON_IRQ_STACK guoren
2022-09-08 16:08   ` Sebastian Andrzej Siewior
2022-09-09  7:30     ` David Laight
2022-09-11  1:13       ` Guo Ren
2022-09-08  2:25 ` [PATCH V4 7/8] riscv: Support HAVE_SOFTIRQ_ON_OWN_STACK guoren
2022-09-08 16:01   ` Sebastian Andrzej Siewior
2022-09-18 15:42     ` Guo Ren
2022-09-08  2:25 ` [PATCH V4 8/8] riscv: Add config of thread stack size guoren
2022-09-08  7:35   ` Arnd Bergmann
2022-09-10 12:52     ` Guo Ren
2022-09-10 16:06       ` Arnd Bergmann [this message]
2022-09-10 23:35         ` Guo Ren
2022-09-11 18:39           ` Arnd Bergmann
2022-09-12  4:14             ` Guo Ren
2022-09-12  8:23               ` Arnd Bergmann
2022-09-19  8:38                 ` Guo Ren
2022-09-19  8:35         ` Guo Ren
2022-09-20  0:46           ` Guo Ren
2022-09-20  7:15             ` Arnd Bergmann
2022-09-21  6:11               ` Guo Ren
2022-09-20  7:17             ` Arnd Bergmann
2022-09-21  6:13               ` Guo Ren
2022-09-21  8:23                 ` Guo Ren
2022-09-21 10:31                   ` Guo Ren
2022-09-21 10:46                     ` Guo Ren
2022-09-22  5:55                       ` Arnd Bergmann

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