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From: Nam Cao <namcao@linutronix.de>
To: litaliano00 <litaliano00.contact@gmail.com>
Cc: palmer@dabbelt.com, pjw@kernel.org, aou@eecs.berkeley.edu,
	alex@ghiti.fr, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: Add WFI to secondary hart spinwait loop
Date: Tue, 07 Apr 2026 13:48:41 +0200	[thread overview]
Message-ID: <87tstnuh2e.fsf@yellow.woof> (raw)
In-Reply-To: <CAK-CEVO6h+v-2iRdsR6THbOvoTrxM7xnmsDyXfnP5sAgUdmhYQ@mail.gmail.com>

litaliano00 <litaliano00.contact@gmail.com> writes:
> You are correct to question this. There is no interrupt sent to the
> waiting harts in the current spinwait design — the primary hart simply
> writes to __cpu_spinwait_stack_pointer and __cpu_spinwait_task_pointer.
> A bare WFI would cause secondary harts to sleep indefinitely since no
> IPI is issued after those writes.
>
> The correct fix would require the primary hart to send an IPI to all
> waiting harts after populating the pointers, which is a more involved
> change. The current patch is insufficient as-is.

Yeah, that's also what I would do.

> I will send a v2 that reverts this change. Apologies for the noise.

There's no need for that, this patch has not been applied.

Best regards,
Nam

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WARNING: multiple messages have this Message-ID (diff)
From: Nam Cao <namcao@linutronix.de>
To: litaliano00 <litaliano00.contact@gmail.com>
Cc: palmer@dabbelt.com, pjw@kernel.org, aou@eecs.berkeley.edu,
	alex@ghiti.fr, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: Add WFI to secondary hart spinwait loop
Date: Tue, 07 Apr 2026 13:48:41 +0200	[thread overview]
Message-ID: <87tstnuh2e.fsf@yellow.woof> (raw)
In-Reply-To: <CAK-CEVO6h+v-2iRdsR6THbOvoTrxM7xnmsDyXfnP5sAgUdmhYQ@mail.gmail.com>

litaliano00 <litaliano00.contact@gmail.com> writes:
> You are correct to question this. There is no interrupt sent to the
> waiting harts in the current spinwait design — the primary hart simply
> writes to __cpu_spinwait_stack_pointer and __cpu_spinwait_task_pointer.
> A bare WFI would cause secondary harts to sleep indefinitely since no
> IPI is issued after those writes.
>
> The correct fix would require the primary hart to send an IPI to all
> waiting harts after populating the pointers, which is a more involved
> change. The current patch is insufficient as-is.

Yeah, that's also what I would do.

> I will send a v2 that reverts this change. Apologies for the noise.

There's no need for that, this patch has not been applied.

Best regards,
Nam

  parent reply	other threads:[~2026-04-07 11:48 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-04-07  7:45 [PATCH] riscv: Add WFI to secondary hart spinwait loop Adriano Vero
2026-04-07  7:45 ` Adriano Vero
2026-04-07  8:40 ` Nam Cao
2026-04-07  8:40   ` Nam Cao
2026-04-07  8:45 ` Nam Cao
2026-04-07  8:45   ` Nam Cao
     [not found]   ` <CAK-CEVO6h+v-2iRdsR6THbOvoTrxM7xnmsDyXfnP5sAgUdmhYQ@mail.gmail.com>
2026-04-07 11:48     ` Nam Cao [this message]
2026-04-07 11:48       ` Nam Cao
     [not found] ` <8c77810f-8198-46b5-9b6b-23095dbfee1a@lanxincomputing.com>
2026-04-07 12:27   ` litaliano00
2026-04-07 12:27     ` litaliano00

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