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Date:   Tue, 27 Aug 2019 22:14:17 +0100
From:   Matthew Garrett <mjg59@srcf.ucam.org>
To:     Vineeth Remanan Pillai <vpillai@digitalocean.com>
Cc:     Nishanth Aravamudan <naravamudan@digitalocean.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Tim Chen <tim.c.chen@linux.intel.com>, mingo@kernel.org,
        tglx@linutronix.de, pjt@google.com, torvalds@linux-foundation.org,
        linux-kernel@vger.kernel.org, subhra.mazumdar@oracle.com,
        fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com,
        Phil Auld <pauld@redhat.com>, Aaron Lu <aaron.lwe@gmail.com>,
        Aubrey Li <aubrey.intel@gmail.com>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [RFC PATCH v3 00/16] Core scheduling v3
Message-ID: <20190827211417.snpwgnhsu5t6u52y@srcf.ucam.org>
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Apple have provided a sysctl that allows applications to indicate that 
specific threads should make use of core isolation while allowing 
the rest of the system to make use of SMT, and browsers (Safari, Firefox 
and Chrome, at least) are now making use of this. Trying to do something 
similar using cgroups seems a bit awkward. Would something like this be 
reasonable? Having spoken to the Chrome team, I believe that the 
semantics we want are:

1) A thread to be able to indicate that it should not run on the same 
core as anything not in posession of the same cookie
2) Descendents of that thread to (by default) have the same cookie
3) No other thread be able to obtain the same cookie
4) Threads not be able to rejoin the global group (ie, threads can 
segregate themselves from their parent and peers, but can never rejoin 
that group once segregated)

but don't know if that's what everyone else would want.

diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 094bb03b9cc2..5d411246d4d5 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -229,4 +229,5 @@ struct prctl_mm_map {
 # define PR_PAC_APDBKEY			(1UL << 3)
 # define PR_PAC_APGAKEY			(1UL << 4)
 
+#define PR_CORE_ISOLATE			55
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 12df0e5434b8..a054cfcca511 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2486,6 +2486,13 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			return -EINVAL;
 		error = PAC_RESET_KEYS(me, arg2);
 		break;
+	case PR_CORE_ISOLATE:
+#ifdef CONFIG_SCHED_CORE
+		current->core_cookie = (unsigned long)current;
+#else
+		result = -EINVAL;
+#endif
+		break;
 	default:
 		error = -EINVAL;
 		break;


-- 
Matthew Garrett | mjg59@srcf.ucam.org