From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Dagaen Golomb <dgolomb@seas.upenn.edu>
Cc: Juergen Gross <jgross@suse.com>, Xen-devel@lists.xen.org
Subject: Re: Elaboration of "Question about sharing spinlock_t among VMs in Xen"
Date: Mon, 27 Jun 2016 15:09:24 -0400 [thread overview]
Message-ID: <20160627190924.GB21942@char.us.oracle.com> (raw)
In-Reply-To: <CALcuvTghLzyE13by5ZEoSPWEERVZKt=zdPp45-Rc_v9g5oRi5Q@mail.gmail.com>
> > One other thing you should be aware of: as soon as one of your guests
> > has only one vcpu it will drop the "lock" prefixes for updates of the
> > lock word. So there will be a chance of races just because one or both
> > guests are thinking no other cpu can access the lock word concurrently.
>
> Now that is an interesting point! I am indeed using 1 vcpu for each
> domain right now. Does it automatically drop lock if it detects one
> vcpu when booting? Or is this set at compile time? Shouldn't setting
It does patching of the binary during bootup time.
You can disable the patching by using noreplace-smp on Linux command line.
> SMP to y regardless of core/vcpu count keep the SMP spinlock
> implementation? I definitely did not think about this -- It was
> compiled with one vcpu so if its done at compile time this could be
> the issue. I doubt its done at boot but if so I would presume there is
> a way to disable this?
>
> Below is the config file grepped for "SMP".
> CONFIG_X86_64_SMP=y
> CONFIG_GENERIC_SMP_IDLE_THREAD=y
> CONFIG_SMP=y
> # CONFIG_X86_VSMP is not set
> # CONFIG_MAXSMP is not set
> CONFIG_PM_SLEEP_SMP=y
>
> See anything problematic? Seems PV spinlocks is not set, and SMP is
> enabled... or is something else required to prevent stripping the
> spinlocks? Also not sure if any of the set SPIN config items could
> mess with this. If this is done at boot, a point in the direction for
> preventing this would be appreciated!
>
> Regards,
> Dagaen Golomb
> Ph.D Student, University of Pennsylvania
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next prev parent reply other threads:[~2016-06-27 19:09 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-27 2:44 Elaboration of "Question about sharing spinlock_t among VMs in Xen" Dagaen Golomb
2016-06-27 14:08 ` Konrad Rzeszutek Wilk
2016-06-27 15:24 ` Dagaen Golomb
2016-06-27 18:22 ` Juergen Gross
2016-06-27 18:40 ` Dagaen Golomb
2016-06-27 19:09 ` Konrad Rzeszutek Wilk [this message]
2016-06-27 19:12 ` Dagaen Golomb
2016-06-27 19:59 ` Dagaen Golomb
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