From: Ingo Molnar <mingo@kernel.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Davidlohr Bueso <dave@stgolabs.net>,
Linux-RT <linux-rt-users@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] locking/rwbase: Prevent indefinite writer starvation
Date: Wed, 18 Jan 2023 11:45:45 +0100 [thread overview]
Message-ID: <Y8fN2VQQTGUZ3ykw@gmail.com> (raw)
In-Reply-To: <20230117165021.t5m7c2d6frbbfzig@techsingularity.net>
* Mel Gorman <mgorman@techsingularity.net> wrote:
> > > dio_truncate is not a realtime application but indefinite writer
> > > starvation
> >
> > If so then the PI boosting would not work if we would have it ;)
> >
>
> True, but it's still undesirable for a basic functional test using normal
> tasks with no prioritisation to stall forever.
Agreed.
> +/*
> + * Allow reader bias with a pending writer for a minimum of 4ms or 1 tick.
> + * This matches RWSEM_WAIT_TIMEOUT for the generic RWSEM implementation.
> + * The granularity is not exact as the lowest bit in rwbase_rt->waiter_timeout
> + * is used to detect recent DL / RT tasks taking a read lock.
> + */
> +#define RWBASE_RT_WAIT_TIMEOUT DIV_ROUND_UP(HZ, 250)
> +
> +static void __sched update_dlrt_reader(struct rwbase_rt *rwb)
> +{
> + /* No update required if DL / RT tasks already identified. */
> + if (rwb->waiter_timeout & 1)
> + return;
> +
> + /*
> + * Record a DL / RT task acquiring the lock for read. This may result
> + * in indefinite writer starvation but DL / RT tasks should avoid such
> + * behaviour.
> + */
> + if (rt_task(current)) {
> + struct rt_mutex_base *rtm = &rwb->rtmutex;
> + unsigned long flags;
> +
> + raw_spin_lock_irqsave(&rtm->wait_lock, flags);
> + rwb->waiter_timeout |= 1;
> + raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
> + }
> +}
So I'm not sure this should be dependent on the task being an RT task.
Starvation scenarios are bad no matter what scheduling policy is used.
Should be unconditional - and all workloads should live with the new
behavior.
Thanks,
Ingo
next prev parent reply other threads:[~2023-01-18 11:28 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-17 8:38 [PATCH v2] locking/rwbase: Prevent indefinite writer starvation Mel Gorman
[not found] ` <20230117105031.2512-1-hdanton@sina.com>
2023-01-17 12:18 ` Mel Gorman
2023-01-17 14:22 ` Sebastian Andrzej Siewior
2023-01-17 16:50 ` Mel Gorman
2023-01-18 10:45 ` Ingo Molnar [this message]
2023-01-18 16:00 ` Mel Gorman
2023-01-18 15:25 ` Sebastian Andrzej Siewior
2023-01-18 17:31 ` Mel Gorman
2023-01-19 8:25 ` Sebastian Andrzej Siewior
2023-01-19 11:02 ` Mel Gorman
2023-01-19 16:28 ` Sebastian Andrzej Siewior
2023-01-19 17:41 ` Mel Gorman
2023-01-19 17:48 ` Davidlohr Bueso
2023-01-19 17:58 ` Davidlohr Bueso
2023-01-20 8:25 ` Sebastian Andrzej Siewior
2023-01-20 13:24 ` Mel Gorman
2023-01-20 13:38 ` Sebastian Andrzej Siewior
2023-01-20 14:07 ` Mel Gorman
2023-01-20 15:36 ` Davidlohr Bueso
[not found] ` <20230119011538.3247-1-hdanton@sina.com>
2023-01-19 8:32 ` Sebastian Andrzej Siewior
[not found] ` <20230119135903.3524-1-hdanton@sina.com>
2023-01-19 16:36 ` Sebastian Andrzej Siewior
[not found] ` <20230120093711.3862-1-hdanton@sina.com>
2023-01-20 18:34 ` Sebastian Andrzej Siewior
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Y8fN2VQQTGUZ3ykw@gmail.com \
--to=mingo@kernel.org \
--cc=bigeasy@linutronix.de \
--cc=dave@stgolabs.net \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rt-users@vger.kernel.org \
--cc=mgorman@techsingularity.net \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).