linux-kernel - Re: [PATCH] riscv: keep interrupts disabled for BREAKPOINT exception

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Date:   Fri, 9 Apr 2021 00:45:13 +0200 (CEST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Masami Hiramatsu <mhiramat@...nel.org>
cc:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
        Jisheng Zhang <jszhang3@...l.ustc.edu.cn>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Guo Ren <guoren@...ux.alibaba.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: keep interrupts disabled for BREAKPOINT
 exception

On Fri, 9 Apr 2021, Masami Hiramatsu wrote:

> > >  Is this approach guaranteed to keep interrupt handling latency low enough
> > > for the system not to be negatively affected, e.g. for the purpose of NTP
> > > timekeeping?
> > 
> > IMHO, interrupt latency can't be ensured if kprobes is triggered.
> 
> Indeed. The latency depends on what the kprobe user handler does. Of course
> it must be as minimal as possible... On x86, it is less than a few microseconds.
> Thus it may be a jitter on hard realtime system, but not a big issue on
> usual system like NTP timekeeping.

 Ack.  Assuming that the breakpoint exception will only disable interrupts 
if kprobes are in use it seems reasonable to me.

 Thanks for double-checking.

  Maciej