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From: Paul Walmsley <pjw@kernel.org>
To: Josephine Pfeiffer <hi@josie.lol>
Cc: paul.walmsley@sifive.com, palmer@dabbelt.com,
	aou@eecs.berkeley.edu,  alex@ghiti.fr,
	linux-riscv@lists.infradead.org,  linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] riscv: ptdump: use seq_puts() in pt_dump_seq_puts() macro
Date: Sat, 18 Oct 2025 18:21:52 -0600 (MDT)	[thread overview]
Message-ID: <2eaeaa69-b2cf-3a3a-0239-2aefcaa836aa@kernel.org> (raw)
In-Reply-To: <20251018170451.3355496-1-hi@josie.lol>

On Sat, 18 Oct 2025, Josephine Pfeiffer wrote:

> The pt_dump_seq_puts() macro incorrectly uses seq_printf() instead of
> seq_puts(). This is both a performance issue and conceptually wrong,
> as the macro name suggests plain string output (puts) but the
> implementation uses formatted output (printf).
> 
> The macro is used in ptdump.c:301 to output a newline character. Using
> seq_printf() adds unnecessary overhead for format string parsing when
> outputting this constant string.

Hard to accept that it's a performance issue.  But I think you're right 
that generating a newline should be done with seq_puts().

> This bug was introduced in commit 59c4da8640cc ("riscv: Add support to
> dump the kernel page tables") in 2020, which copied the implementation
> pattern from other architectures that had the same bug.
> 
> Fixes: 59c4da8640cc ("riscv: Add support to dump the kernel page tables")
> Signed-off-by: Josephine Pfeiffer <hi@josie.lol>

A better fix would seem to be to just get rid of pt_dump_seq_puts().  It's 
only used once in arch/riscv.

Taking a broader view, both pt_dump_seq_puts() and pt_dump_seq_printf() 
look completely pointless.  Is there any argument for keeping them?


- Paul

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linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

WARNING: multiple messages have this Message-ID (diff)
From: Paul Walmsley <pjw@kernel.org>
To: Josephine Pfeiffer <hi@josie.lol>
Cc: paul.walmsley@sifive.com, palmer@dabbelt.com,
	aou@eecs.berkeley.edu,  alex@ghiti.fr,
	linux-riscv@lists.infradead.org,  linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] riscv: ptdump: use seq_puts() in pt_dump_seq_puts() macro
Date: Sat, 18 Oct 2025 18:21:52 -0600 (MDT)	[thread overview]
Message-ID: <2eaeaa69-b2cf-3a3a-0239-2aefcaa836aa@kernel.org> (raw)
In-Reply-To: <20251018170451.3355496-1-hi@josie.lol>

On Sat, 18 Oct 2025, Josephine Pfeiffer wrote:

> The pt_dump_seq_puts() macro incorrectly uses seq_printf() instead of
> seq_puts(). This is both a performance issue and conceptually wrong,
> as the macro name suggests plain string output (puts) but the
> implementation uses formatted output (printf).
> 
> The macro is used in ptdump.c:301 to output a newline character. Using
> seq_printf() adds unnecessary overhead for format string parsing when
> outputting this constant string.

Hard to accept that it's a performance issue.  But I think you're right 
that generating a newline should be done with seq_puts().

> This bug was introduced in commit 59c4da8640cc ("riscv: Add support to
> dump the kernel page tables") in 2020, which copied the implementation
> pattern from other architectures that had the same bug.
> 
> Fixes: 59c4da8640cc ("riscv: Add support to dump the kernel page tables")
> Signed-off-by: Josephine Pfeiffer <hi@josie.lol>

A better fix would seem to be to just get rid of pt_dump_seq_puts().  It's 
only used once in arch/riscv.

Taking a broader view, both pt_dump_seq_puts() and pt_dump_seq_printf() 
look completely pointless.  Is there any argument for keeping them?


- Paul

  reply	other threads:[~2025-10-19  0:22 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-10-18 17:04 [PATCH 3/4] riscv: ptdump: use seq_puts() in pt_dump_seq_puts() macro Josephine Pfeiffer
2025-10-18 17:04 ` Josephine Pfeiffer
2025-10-19  0:21 ` Paul Walmsley [this message]
2025-10-19  0:21   ` Paul Walmsley
2025-10-19 14:07   ` Josephine Pfeiffer
2025-10-19 14:07     ` Josephine Pfeiffer
2025-10-25  7:15     ` Paul Walmsley
2025-10-25  7:15       ` Paul Walmsley

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