Re: [Xen-devel] [PATCH v7 03/16] xen: clean up grant_table.h

[Juergen Gross <jgross@xxxxxxxx>]

On 19/09/17 17:55, Jan Beulich wrote:
>>>> On 19.09.17 at 11:58, <jgross@xxxxxxxx> wrote:
>> --- a/xen/common/grant_table.c
>> +++ b/xen/common/grant_table.c
>> @@ -40,6 +40,45 @@
>>  #include <xsm/xsm.h>
>>  #include <asm/flushtlb.h>
>>  
>> +/* Per-domain grant information. */
>> +struct grant_table {
>> +    /*
>> +     * Lock protecting updates to grant table state (version, active
>> +     * entry list, etc.)
>> +     */
>> +    percpu_rwlock_t       lock;
>> +    /* Lock protecting the maptrack limit */
>> +    spinlock_t            maptrack_lock;
> 
> Hmm, I'm not sure about putting two locks so obviously close to one
> another. But then again the structure doesn't look to be larger than
> a cache line anyway, so moving it wouldn't be any win as it seems.

Additionally not many domains need both locks frequently: driver domains
(including dom0) use the maptrack_lock mostly, all other domains won't
use it at all. So I assume conflicts should be really very very rare.

> 
>> @@ -1580,7 +1659,7 @@ gnttab_unpopulate_status_frames(struct domain *d, 
>> struct grant_table *gt)
>>   * Grow the grant table. The caller must hold the grant table's
>>   * write lock before calling this function.
>>   */
>> -int
>> +static int
>>  gnttab_grow_table(struct domain *d, unsigned int req_nr_frames)
>>  {
> 
> Wouldn't this better be part of patch 2? But no need to resend
> because of this unless v8 becomes necessary anyway.

Hmm, true. I wanted to send V8 tomorrow due to patch 4 (some leftovers
from patch development in include/public/domctl.h). I'll do the change.


Juergen


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