Re: [PATCH v3] irqchip/gicv3-its: Avoid memory over allocation for ITEs

[Shanker Donthineni]

Hi Marc,


On 03/17/2017 08:50 AM, Marc Zyngier wrote:
> On 07/03/17 14:25, Shanker Donthineni wrote:
>> We are always allocating extra 255Bytes of memory to handle ITE
>> physical address alignment requirement. The kmalloc() satisfies
>> the ITE alignment since the ITS driver is requesting a minimum
>> size of ITS_ITT_ALIGN bytes.
>>
>> Let's try to allocate the exact amount of memory that is required
>> for ITEs to avoid wastage.
>>
>> Signed-off-by: Shanker Donthineni <shankerd@xxxxxxxxxxxxxx>
>> ---Hi 
>> v2: removed 'Change-Id: Ia8084189833f2081ff13c392deb5070c46a64038' from commit.
>> v3: changed from IITE to ITE.
>>
>>  drivers/irqchip/irq-gic-v3-its.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index 86bd428..5aeca78 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -1329,8 +1329,13 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
>>  	 */
>>  	nr_ites = max(2UL, roundup_pow_of_two(nvecs));
>>  	sz = nr_ites * its->ite_size;
>> -	sz = max(sz, ITS_ITT_ALIGN) + ITS_ITT_ALIGN - 1;
>> +	sz = max(sz, ITS_ITT_ALIGN);
>>  	itt = kzalloc(sz, GFP_KERNEL);
>> +	if (itt && !IS_ALIGNED(virt_to_phys(itt), ITS_ITT_ALIGN)) {
>> +		kfree(itt);
>> +		itt = kzalloc(sz + ITS_ITT_ALIGN - 1, GFP_KERNEL);
>> +	}
>> +
> Is this really worth the complexity? Are you aware of a system where the
> accumulation of overallocation actually shows up as being an issue?

As such there is no issue with over allocation. Actually this change masked QDF2400 bug 'iirqchip/gicv3-its: Add workaround for QDF2400 ITS erratum 0065' till now, found and fixed recently while looking at the code for possible memory optimizations.
 
> If you want to be absolutely exact in your allocation, then I'd suggest
> doing it all the time, and have a proper dedicated allocator that always
> do the right thing, without a wasteful fallback like you still have here.

We don't need to fallbak, and it can be removed safely. Looking for your suggestion. should I implement a dedicated allocator or remove fallbak for simpler code?

> Thanks,
>
> 	M.

-- 
Shanker Donthineni
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.