linux-kernel - Re: [PATCH] RISCV:IRQ: Support IRQ

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Message-ID: <20190115134108.GA13216@infradead.org>
Date:   Tue, 15 Jan 2019 05:41:08 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     G SatishKumar <gsatish.ldd@...il.com>
Cc:     linux-riscv@...ts.infradead.org, linux-arch@...r.kernel.org,
        palmer@...ive.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] RISCV:IRQ: Support IRQ_WORK interrupts with self IPI

On Sun, Jan 06, 2019 at 07:02:58PM +0530, G SatishKumar wrote:
> 	This patch adds, IRQ Work interrupts support to RISCV arch.
> 
> 	This patch is based on the arm32 patch ARM 7872/1
> 	which ports cleanly.
> 
> 	Done set of changes based on RISCV SMP process.
> 
> 	commit bf18525fd793 ("ARM: 7872/1: Support arch_irq_work_raise()
> 		via self IPIs")
> 	Author: Stephen Boyd <sboyd at codeaurora.org>
> 	Date:   Tue Oct 29 20:32:56 2013 +0100
> 
> 	By default, IRQ work is run from the tick interrupt (see
> 	irq_work_run() in update_process_times()). When we're in full
> 	NOHZ mode, restarting the tick requires the use of IRQ work and
> 	if the only place we run IRQ work is in the tick interrupt we
> 	have an unbreakable cycle. Implement arch_irq_work_raise() via
> 	self IPIs to break this cycle and get the tick started again.
> 	Note that we implement this via IPIs which are only available on
> 	SMP builds. This shouldn't be a problem because full NOHZ is only
> 	supported on SMP builds anyway.

The commit logs here looks oddly indented.  Also what workload did you
test this with?