linux-kernel - Re: [Xen-devel] Performance overhead of paravirt

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 15 May 2009 11:50:48 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jan Beulich <JBeulich@...ell.com>
CC:	Ingo Molnar <mingo@...e.hu>, Jun Nakajima <jun.nakajima@...el.com>,
	Xiaohui Xin <xiaohui.xin@...el.com>, Xin Li <xin.li@...el.com>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [Xen-devel] Performance overhead of paravirt_ops on		 nativeidentified

Jan Beulich wrote:
> A patch for the pv-ops kernel would require some time. What I can give you
> right away - just for reference - are the sources we currently use in our kernel:
> attached.

Hm, I see.  Putting a call out to a pv-ops function in the ticket lock 
slow path looks pretty straightforward.  The need for an extra lock on 
the contended unlock side is a bit unfortunate; have you measured to see 
what hit that has?  Seems to me like you could avoid the problem by 
using per-cpu storage rather than stack storage (though you'd need to 
copy the per-cpu data to stack when handling a nested spinlock).

What's the thinking behind the xen_spin_adjust() stuff?

> static __always_inline void __ticket_spin_lock(raw_spinlock_t *lock) { 
> unsigned int token, count; bool free; __ticket_spin_lock_preamble; if 
> (unlikely(!free)) token = xen_spin_adjust(lock, token); do { count = 1 
> << 10; __ticket_spin_lock_body; } while (unlikely(!count) && 
> !xen_spin_wait(lock, token)); } 

How does this work?  Doesn't it always go into the slowpath loop even if 
the preamble got the lock with no contention?

    J
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/