Re: [PATCHv2 1/1] locking/qspinlock/x86: Avoid test-and-set when PV_DEDICATED is set

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 02/11/2017 19:08, Eduardo Valentin wrote:
> On Thu, Nov 02, 2017 at 06:56:46PM +0100, Paolo Bonzini wrote:
>> On 02/11/2017 18:45, Eduardo Valentin wrote:
>>> Currently, the existing qspinlock implementation will fallback to
>>> test-and-set if the hypervisor has not set the PV_UNHALT flag.
>>>
>>> This patch gives the opportunity to guest kernels to select
>>> between test-and-set and the regular queueu fair lock implementation
>>> based on the PV_DEDICATED KVM feature flag. When the PV_DEDICATED
>>> flag is not set, the code will still fall back to test-and-set,
>>> but when the PV_DEDICATED flag is set, the code will use
>>> the regular queue spinlock implementation.
>>
>> Have you seen Waiman's series that lets you specify this on the guest
>> command line instead?  Would this be acceptable for your use case?
> 
> No, can you please share a link to it? is it already merged to tip/master?

[PATCH-tip v2 0/2] x86/paravirt: Enable users to choose PV lock type
https://lkml.org/lkml/2017/11/1/655

>> (In other words, is there a difference for you between making the host
>> vs. guest administrator toggle the feature?  "@amazon.com" means you are
>> the host admin, how would you use it?)
> 
> The way I think of this is this is a flag set by host side so the
> guest adapts accordingly.
> 
> If the admin in guest side wants to ignore what the host is
> flagging, that is a different story.

Okay, this makes sense.  But perhaps it should be a separate CPUID leaf,
such as "configuration hints", rather than properly a feature.

Paolo
--
To unsubscribe from this list: send the line "unsubscribe linux-doc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html



[Index of Archives]     [Kernel Newbies]     [Security]     [Netfilter]     [Bugtraq]     [Linux FS]     [Yosemite Forum]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Video 4 Linux]     [Device Mapper]     [Linux Resources]

  Powered by Linux