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From: Dave Hansen <firstname.lastname@example.org> To: Fenghua Yu <email@example.com> Cc: Thomas Gleixner <firstname.lastname@example.org>, Ingo Molnar <email@example.com>, "H. Peter Anvin" <firstname.lastname@example.org>, Ashok Raj <email@example.com>, Ravi V Shankar <firstname.lastname@example.org>, Tony Luck <email@example.com>, Rafael Wysocki <firstname.lastname@example.org>, Arjan van de Ven <email@example.com>, Alan Cox <firstname.lastname@example.org>, x86 <email@example.com>, linux-kernel <firstname.lastname@example.org> Subject: Re: [PATCH 09/15] x86/split_lock: Explicitly enable or disable #AC for split locked accesses Date: Wed, 16 May 2018 09:37:33 -0700 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <20180515172908.GC244301@romley-ivt3.sc.intel.com> On 05/15/2018 10:29 AM, Fenghua Yu wrote: > On Tue, May 15, 2018 at 09:15:16AM -0700, Dave Hansen wrote: >> On 05/14/2018 11:52 AM, Fenghua Yu wrote: >>> By default, we don't set or clear the bit 29 in TEST_CTL MSR 0x33 and >>> the bit is inherited from BIOS/hardware setting. >>> >>> The kernel parameter "split_lock_ac=on/off" explicitly sets or clears >>> the bit during boot time. >> >> The more I think about this... Why do we need this at boot anyway? >> Surely boot-time kernel code can't cause performance issues in the same >> way that untrusted repeated userspace can. Why don't we just let >> userspace turn this on? > > Turning split lock earlier can captuer split lock performance issue > in the boot path. Actually we did find two split lock issues during > boot time by turning on the feature earlier (see patch 4 and 5). Yeah, but you're going to have a pretty hard time arguing that these are even close to the same class of issues that occur when all the CPUs are up and userspace is pounding the system with split locks. It also seems like the kind of thing that deserves to be a debugging option, or Kconfig thing rather than a kernel command-line option that has to live forever.
next prev parent reply other threads:[~2018-05-16 16:37 UTC|newest] Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-05-14 18:52 [PATCH 0/15] x86/split_lock: Enable #AC exception for split locked accesses Fenghua Yu 2018-05-14 18:52 ` [PATCH 01/15] x86/split_lock: Add CONFIG and enumerate #AC exception for split locked access feature Fenghua Yu 2018-05-15 15:36 ` Dave Hansen 2018-05-15 15:41 ` Fenghua Yu 2018-05-15 15:54 ` Dave Hansen 2018-05-14 18:52 ` [PATCH 02/15] x86/split_lock: Set up #AC exception for split locked accesses Fenghua Yu 2018-05-14 18:52 ` [PATCH 03/15] x86/split_lock: Handle #AC exception for split lock in kernel mode Fenghua Yu 2018-05-15 15:51 ` Dave Hansen 2018-05-15 16:35 ` Luck, Tony 2018-05-15 17:21 ` Fenghua Yu 2018-05-16 16:44 ` Dave Hansen 2018-05-16 21:35 ` Fenghua Yu 2018-05-14 18:52 ` [PATCH 04/15] x86/split_lock: Use non locked bit set instruction in set_cpu_cap Fenghua Yu 2018-05-14 18:52 ` [PATCH 05/15] x86/split_lock: Use non atomic set and clear bit instructions to clear cpufeature Fenghua Yu 2018-05-14 18:52 ` [PATCH 06/15] x86/split_lock: Save #AC setting for split lock in BIOS in boot time and restore the setting in reboot Fenghua Yu 2018-05-14 18:52 ` [PATCH 07/15] x86/split_lock: Handle suspend/hibernate and resume Fenghua Yu 2018-05-14 21:42 ` Rafael J. Wysocki 2018-05-14 18:52 ` [PATCH 08/15] x86/split_lock: Set split lock during EFI runtime service Fenghua Yu 2018-05-14 18:52 ` [PATCH 09/15] x86/split_lock: Explicitly enable or disable #AC for split locked accesses Fenghua Yu 2018-05-15 16:15 ` Dave Hansen 2018-05-15 17:29 ` Fenghua Yu 2018-05-16 16:37 ` Dave Hansen [this message] 2018-05-14 18:52 ` [PATCH 10/15] x86/split_lock: Add a sysfs interface to allow user to enable or disable split lock during run time Fenghua Yu 2018-05-14 18:52 ` [PATCH 11/15] x86/split_lock: Add sysfs interface to control user mode behavior Fenghua Yu 2018-05-14 18:52 ` [PATCH 12/15] x86/split_lock: Add sysfs interface to show and control BIOS split lock setting Fenghua Yu 2018-05-14 18:52 ` [PATCH 13/15] x86/split_lock: Trace #AC exception for split lock Fenghua Yu 2018-05-14 18:52 ` [PATCH 14/15] x86/split_lock: Add CONFIG and testing sysfs interface Fenghua Yu 2018-05-14 18:52 ` [PATCH 15/15] x86/split_lock: Add split lock user space test in selftest Fenghua Yu 2018-05-15 15:10 ` [PATCH 0/15] x86/split_lock: Enable #AC exception for split locked accesses Dave Hansen 2018-05-15 16:26 ` Alan Cox 2018-05-15 16:30 ` Dave Hansen
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