linux-kernel - RE: [PATCH v1 03/18] KVM: selftests/kvm_util: helper functions for vcpus and threads

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Date:   Thu, 27 Oct 2022 14:02:29 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     "Christopherson,, Sean" <seanjc@...gle.com>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "vipinsh@...gle.com" <vipinsh@...gle.com>,
        "ajones@...tanamicro.com" <ajones@...tanamicro.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v1 03/18] KVM: selftests/kvm_util: helper functions for
 vcpus and threads

On Thursday, October 27, 2022 8:10 AM, Sean Christopherson wrote:
> On Mon, Oct 24, 2022, Wei Wang wrote:
> > @@ -14,4 +15,23 @@
> >  	for (i = 0, vcpu = vm->vcpus[0];				\
> >  		vcpu && i < KVM_MAX_VCPUS; vcpu = vm->vcpus[++i])
> >
> > +void __pthread_create_with_name(pthread_t *thread, const
> > +pthread_attr_t *attr,
> 
> Can these return pthread_t instead of taking them as a param and have a "void"
> return?  I'm pretty sure pthread_t is an integer type in most implementations,
> i.e. can be cheaply copied by value.

Yes, sounds good.

> 
> > +			void *(*start_routine)(void *), void *arg, char *name);
> 
> Add a typedef for the payload, both to make it harder to screw up, and to make
> the code more readable.  Does pthread really not provide one already?

You meant typedef for start_routine? I searched throughout pthread.h, and didn't find it.
Maybe we could create one here.

> > +void vm_vcpu_threads_create(struct kvm_vm *vm,
> > +		void *(*start_routine)(void *), uint32_t private_data_size)
> 
> I vote (very strongly) to not deal with allocating private data.  The private data
> isn't strictly related to threads, and the vast majority of callers don't need private
> data, i.e. the param is dead weight in most cases.
> 
> And unless I'm missing something, it's trivial to move to a separate helper,
> though honestly even that seems like overkill.
> 
> Wait, looking further, it already is a separate helper...  Forcing a bunch of
> callers to specify '0' just to eliminate one function call in a handful of cases is not
> a good tradeoff.

The intention was to do the allocation within one vm_for_each_vcpu()
iteration when possible. Just a micro-optimization, but no problem, we can keep
them separate if that looks better (simpler).