From: Juergen Gross <jgross@suse.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>,
linux-kernel@vger.kernel.org, x86@kernel.org, hpa@zytor.com,
tglx@linutronix.de, mingo@redhat.com,
xen-devel@lists.xensource.com, konrad.wilk@oracle.com,
david.vrabel@citrix.com, boris.ostrovsky@oracle.com,
chrisw@sous-sol.org, akataria@vmware.com, rusty@rustcorp.com.au,
virtualization@lists.linux-foundation.org, gleb@kernel.org,
pbonzini@redhat.com, kvm@vger.kernel.org
Subject: Re: [PATCH 0/6] x86: reduce paravirtualized spinlock overhead
Date: Mon, 04 May 2015 07:55:07 +0200 [thread overview]
Message-ID: <554709BB.7090400@suse.com> (raw)
In-Reply-To: <55425ADA.4060105@goop.org>
On 04/30/2015 06:39 PM, Jeremy Fitzhardinge wrote:
> On 04/30/2015 03:53 AM, Juergen Gross wrote:
>> Paravirtualized spinlocks produce some overhead even if the kernel is
>> running on bare metal. The main reason are the more complex locking
>> and unlocking functions. Especially unlocking is no longer just one
>> instruction but so complex that it is no longer inlined.
>>
>> This patch series addresses this issue by adding two more pvops
>> functions to reduce the size of the inlined spinlock functions. When
>> running on bare metal unlocking is again basically one instruction.
>
> Out of curiosity, is there a measurable difference?
I did a small measurement of the pure locking functions on bare metal
without and with my patches.
spin_lock() for the first time (lock and code not in cache) dropped from
about 600 to 500 cycles.
spin_unlock() for first time dropped from 145 to 87 cycles.
spin_lock() in a loop dropped from 48 to 45 cycles.
spin_unlock() in the same loop dropped from 24 to 22 cycles.
Juergen
next prev parent reply other threads:[~2015-05-04 5:55 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-30 10:53 [PATCH 0/6] x86: reduce paravirtualized spinlock overhead Juergen Gross
2015-04-30 10:53 ` [PATCH 1/6] x86: use macro instead of "0" for setting TICKET_SLOWPATH_FLAG Juergen Gross
2015-04-30 10:53 ` [PATCH 2/6] x86: move decision about clearing slowpath flag into arch_spin_lock() Juergen Gross
2015-04-30 10:54 ` [PATCH 3/6] x86: introduce new pvops function clear_slowpath Juergen Gross
2015-04-30 10:54 ` [PATCH 4/6] x86: introduce new pvops function spin_unlock Juergen Gross
2015-04-30 10:54 ` [PATCH 5/6] x86: switch config from UNINLINE_SPIN_UNLOCK to INLINE_SPIN_UNLOCK Juergen Gross
2015-04-30 10:54 ` [PATCH 6/6] x86: remove no longer needed paravirt_ticketlocks_enabled Juergen Gross
2015-04-30 16:39 ` [PATCH 0/6] x86: reduce paravirtualized spinlock overhead Jeremy Fitzhardinge
2015-05-04 5:55 ` Juergen Gross [this message]
2015-05-05 17:21 ` Jeremy Fitzhardinge
2015-05-06 11:55 ` Juergen Gross
2015-05-17 5:30 ` Ingo Molnar
2015-05-18 8:11 ` Juergen Gross
2015-05-15 12:16 ` Juergen Gross
2015-06-08 4:09 ` Juergen Gross
2015-06-16 14:37 ` Juergen Gross
2015-06-16 15:18 ` Thomas Gleixner
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