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SubjectRe: [PATCH v3] irqchip/gicv3-its: Avoid memory over allocation for ITEs
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Hi Marc,


On 03/20/2017 05:14 AM, Shanker Donthineni wrote:
> Hi Marc,
>
>
> On 03/17/2017 10:33 AM, Marc Zyngier wrote:
>> On 17/03/17 14:18, Shanker Donthineni wrote:
>>> 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@codeaurora.org>
>>>>> ---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?
>> Are you saying that kmalloc is guaranteed to give us something that is
>> 256 byte aligned? If so, why do we test for alignment (with free +
>> over-allocate if it fails)?
> I've verified on my system kmalloc() is always allocating memory with 256bytes alignment. kmalloc() uses the generic slab caches available in the kernel to allocate memory based on the input size.
>
>> I'd rather have only one way of allocating the ITT. Either we always
>> overallocate in order to guarantee right alignment (and my personal view
>> is that for most system, this doesn't matter at all), or we create our
>> own allocator. The issue with the latter is that we don't really have a
>> good story for allocating arrays of objects with a given alignment
>> (kmem_cache_* only deals with single objects).
> Adding a dedicated function to allocate memory is preferable but need pull a few of lines of code.
>
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index a27a074..f0125e5 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -90,6 +90,8 @@ struct its_node {
> u32 ite_size;
> u32 device_ids;
> int numa_node;
> + struct page *ite_page;
> + u32 ite_psz;
> };
>
> #define ITS_ITT_ALIGN SZ_256
> @@ -266,7 +268,6 @@ static struct its_collection *its_build_mapd_cmd(struct its_cmd_block *cmd,
> u8 size = ilog2(desc->its_mapd_cmd.dev->nr_ites);
>
> itt_addr = virt_to_phys(desc->its_mapd_cmd.dev->itt);
> - itt_addr = ALIGN(itt_addr, ITS_ITT_ALIGN);
>
> its_encode_cmd(cmd, GITS_CMD_MAPD);
> its_encode_devid(cmd, desc->its_mapd_cmd.dev->device_id);
> @@ -1319,6 +1320,42 @@ static bool its_alloc_device_table(struct its_node *its, u32 dev_id)
> return true;
> }
>
> +static void *its_alloc_memory_ites(struct its_node *its, int nr_ites)
> +{
> + unsigned long flags;
> + struct page *page;
> + void *ite;
> + u32 size;
> +
> + size = ALIGN(nr_ites * its->ite_size, ITS_ITT_ALIGN);
> + raw_spin_lock_irqsave(&its->lock, flags);
> +
> + /* Try to reuse the current page if enough space is available */
> + if (size > its->ite_psz) {
> + /* Allocate a new compound page with minimum order 1 */
> + page = alloc_pages(GFP_KERNEL | __GFP_COMP | __GFP_ZERO,
> + max(get_order(size), 1));
> + if (!page) {
> + raw_spin_unlock_irqrestore(&its->lock, flags);
> + return NULL;
> + }
> +
> + /* Free current page, decrement page count */
> + if (its->ite_page)
> + put_page(its->ite_page);
> + its->ite_psz = PAGE_ORDER_TO_SIZE(compound_order(page));
> + its->ite_page = page;
> + }
> +
> + get_page(its->ite_page); /* increment page count */
> + its->ite_psz -= size; /* update free space */
> + ite = page_address(its->ite_page) + its->ite_psz;
> + raw_spin_unlock_irqrestore(&its->lock, flags);
> + gic_flush_dcache_to_poc(ite, size);
> +
> + return ite;
> +}
> +
> static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
> int nvecs)
> {
> @@ -1330,7 +1367,6 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
> int lpi_base;
> int nr_lpis;
> int nr_ites;
> - int sz;
>
> if (!its_alloc_device_table(its, dev_id))
> return NULL;
> @@ -1342,22 +1378,22 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
> * express an ITT with a single entry.
> */
> 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;
> - itt = kzalloc(sz, GFP_KERNEL);
> + itt = its_alloc_memory_ites(its, nr_ites);
> + if (!itt)
> + return NULL;
> +
> lpi_map = its_lpi_alloc_chunks(nvecs, &lpi_base, &nr_lpis);
> if (lpi_map)
> col_map = kzalloc(sizeof(*col_map) * nr_lpis, GFP_KERNEL);
>
> - if (!dev || !itt || !lpi_map || !col_map) {
> + if (!dev || !lpi_map || !col_map) {
> kfree(dev);
> - kfree(itt);
> + put_page(virt_to_page(itt));
> kfree(lpi_map);
> kfree(col_map);
> return NULL;
> }
>
> - gic_flush_dcache_to_poc(itt, sz);
>
> dev->its = its;
> dev->itt = itt;
> @@ -1386,7 +1422,7 @@ static void its_free_device(struct its_device *its_dev)
> raw_spin_lock_irqsave(&its_dev->its->lock, flags);
> list_del(&its_dev->entry);
> raw_spin_unlock_irqrestore(&its_dev->its->lock, flags);
> - kfree(its_dev->itt);
> + put_page(virt_to_page(its_dev->itt));
> kfree(its_dev);
> }
>
>
>

This patch is not urgent, if you want we can revisit it at later time.

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);
+ }
+
lpi_map = its_lpi_alloc_chunks(nvecs, &lpi_base, &nr_lpis);
if (lpi_map)
col_map = kzalloc(sizeof(*col_map) * nr_lpis, GFP_KERNEL);
--
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.

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