linux-kernel - Re: [PATCH v5 1/1] blktrace: switch trace spinlock to a raw spinlock

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Message-ID: <8340efc7-f922-fb8c-772c-de72cefe3470@kernel.dk>
Date:   Mon, 20 Dec 2021 12:38:22 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Wander Lairson Costa <wander@...hat.com>,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "open list:BLOCK LAYER" <linux-block@...r.kernel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH v5 1/1] blktrace: switch trace spinlock to a raw spinlock

On 12/20/21 12:28 PM, Wander Lairson Costa wrote:
> The running_trace_lock protects running_trace_list and is acquired
> within the tracepoint which implies disabled preemption. The spinlock_t
> typed lock can not be acquired with disabled preemption on PREEMPT_RT
> because it becomes a sleeping lock.
> The runtime of the tracepoint depends on the number of entries in
> running_trace_list and has no limit. The blk-tracer is considered debug
> code and higher latencies here are okay.

You didn't put a changelog in here. Was this one actually compiled? Was
it runtime tested?

-- 
Jens Axboe