Re: [Xen-devel] [PATCH v12 for-xen-4.5 11/20] x86/VPMU: Interface for setting PMU mode and flags

[Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>]

Am Montag 29 September 2014, 09:56:50 schrieb Boris Ostrovsky:
> On 09/29/2014 09:25 AM, Dietmar Hahn wrote:
> > +static int vpmu_force_context_switch(void)
> > +{
> > +    unsigned i, j, allbutself_num, mycpu;
> > +    static s_time_t start, now;
> > +    struct tasklet **sync_task;
> > +    struct vcpu *curr_vcpu = current;
> > +    int ret = 0;
> > +
> > +    allbutself_num = num_online_cpus() - 1;
> > +
> > +    sync_task = xzalloc_array(struct tasklet *, allbutself_num);
> > +    if ( !sync_task )
> > +    {
> > +        printk(XENLOG_WARNING "vpmu_force_context_switch: out of 
> > memory\n");
> > +        return -ENOMEM;
> > +    }
> > +
> > +    for ( i = 0; i < allbutself_num; i++ )
> > +    {
> > +        sync_task[i] = xmalloc(struct tasklet);
> > +        if ( sync_task[i] == NULL )
> > +        {
> > +            printk(XENLOG_WARNING "vpmu_force_context_switch: out of 
> > memory\n");
> > +            ret = -ENOMEM;
> > +            goto out;
> > +        }
> > +        tasklet_init(sync_task[i], vpmu_sched_checkin, 0);
> > Only a question of understanding.
> > Is there a special reason not to use a single memory allocation
> > except for memory fragmentation on systems with a large number of cpus?
> >
> >       struct tasklet *sync_task;
> >       sync_task = xmalloc(sizeof(struct tasklet) * allbutself_num);
> 
> 
> Exactly because of fragmentation -- this will avoid asking for more than 
> a page during runtime. I, in fact, originally had it allocated as a 
> single chunk, just as you suggested above, but Jan asked this to be 
> split into smaller, sub-page pieces.
> 
> -boris

OK, then I overlooked this :-(
Sorry for the noise!
Dietmar.

> 
> 
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> 

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