Date: Thu, 19 Feb 2015 22:26:09 +0100 (CET)
From: Jiri Kosina <jkosina@suse.cz>
To: Josh Poimboeuf <jpoimboe@redhat.com>
cc: Vojtech Pavlik <vojtech@suse.com>, Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, Seth Jennings <sjenning@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] sched: add sched_task_call()
In-Reply-To: <20150219173255.GC15980@treble.redhat.com>
Message-ID: <alpine.LNX.2.00.1502192223070.28769@pobox.suse.cz>
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On Thu, 19 Feb 2015, Josh Poimboeuf wrote:

> How about with a TIF_IN_USERSPACE thread flag?  It could be cleared/set
> right at the border.  Then for running tasks it's as simple as:
> 
> if (test_tsk_thread_flag(task, TIF_IN_USERSPACE))
> 	klp_switch_task_universe(task);

That's in principle what CONTEXT_TRACKING is doing, i.e. the condition 
we'd be interested in would be

	__this_cpu_read(context_tracking.state) == IN_USER

But it has overhead.

-- 
Jiri Kosina
SUSE Labs
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