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Date: Wed, 19 Oct 2022 08:26:19 +0800
From: Gavin Shan <gshan@...hat.com>
To: "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
Cc: kvm@...r.kernel.org, maz@...nel.org, linux-kernel@...r.kernel.org,
zhenyzha@...hat.com, shan.gavin@...il.com, kvmarm@...ts.linux.dev,
pbonzini@...hat.com, shuah@...nel.org,
kvmarm@...ts.cs.columbia.edu, ajones@...tanamicro.com
Subject: Re: [PATCH 4/6] KVM: selftests: memslot_perf_test: Support variable
guest page size
On 10/18/22 11:56 PM, Maciej S. Szmigiero wrote:
> On 18.10.2022 02:51, Gavin Shan wrote:
>> On 10/18/22 8:46 AM, Gavin Shan wrote:
>>> On 10/18/22 5:31 AM, Maciej S. Szmigiero wrote:
>>>> On 14.10.2022 09:19, Gavin Shan wrote:
>>>>> The test case is obviously broken on aarch64 because non-4KB guest
>>>>> page size is supported. The guest page size on aarch64 could be 4KB,
>>>>> 16KB or 64KB.
>>>>>
>>>>> This supports variable guest page size, mostly for aarch64.
>>>>>
>>>>> - The host determines the guest page size when virtual machine is
>>>>> created. The value is also passed to guest through the synchronization
>>>>> area.
>>>>>
>>>>> - The number of guest pages are unknown until the virtual machine
>>>>> is to be created. So all the related macros are dropped. Instead,
>>>>> their values are dynamically calculated based on the guest page
>>>>> size.
>>>>>
>>>>> - The static checks on memory sizes and pages becomes dependent
>>>>> on guest page size, which is unknown until the virtual machine
>>>>> is about to be created. So all the static checks are converted
>>>>> to dynamic checks, done in check_memory_sizes().
>>>>>
>>>>> - As the address passed to madvise() should be aligned to host page,
>>>>> the size of page chunk is automatically selected, other than one
>>>>> page.
>>>>>
>>>>> - All other changes included in this patch are almost mechanical
>>>>> replacing '4096' with 'guest_page_size'.
>>>>>
>>>>> Signed-off-by: Gavin Shan <gshan@...hat.com>
>>>>> ---
>>>>> .../testing/selftests/kvm/memslot_perf_test.c | 191 +++++++++++-------
>>>>> 1 file changed, 115 insertions(+), 76 deletions(-)
>>>>>
>>>>> diff --git a/tools/testing/selftests/kvm/memslot_perf_test.c b/tools/testing/selftests/kvm/memslot_perf_test.c
>>>>> index d5aa9148f96f..d587bd952ff9 100644
>>>>> --- a/tools/testing/selftests/kvm/memslot_perf_test.c
>>>>> +++ b/tools/testing/selftests/kvm/memslot_perf_test.c
> (...)
>>>>> @@ -77,8 +61,7 @@ static_assert(MEM_TEST_UNMAP_SIZE_PAGES %
>>>>> * for the total size of 25 pages.
>>>>> * Hence, the maximum size here is 50 pages.
>>>>> */
>>>>> -#define MEM_TEST_MOVE_SIZE_PAGES (50)
>>>>> -#define MEM_TEST_MOVE_SIZE (MEM_TEST_MOVE_SIZE_PAGES * 4096)
>>>>> +#define MEM_TEST_MOVE_SIZE 0x32000
>>>>
>>>> The above number seems less readable than an explicit value of 50 pages.
>>>>
>>>> In addition to that, it's 50 pages only with 4k page size, so at least
>>>> the comment above needs to be updated to reflect this fact.
>>>>
>>>
>>> Yeah, I will change the comments like below in next revision.
>>>
>>> /*
>>> * When running this test with 32k memslots, actually 32763 excluding
>>> * the reserved memory slot 0, the memory for each slot is 0x4000 bytes.
>>> * The last slot contains 0x19000 bytes memory. Hence, the maximum size
>>> * here is 0x32000 bytes.
>>> */
>>>
>>
>> I will replace those numbers with readable ones like below :)
>>
>> /*
>> * When running this test with 32k memslots, actually 32763 excluding
>> * the reserved memory slot 0, the memory for each slot is 16KB. The
>> * last slot contains 100KB memory with the remaining 84KB. Hence,
>> * the maximum size is double of that (200KB)
>> */
>
> Still, these numbers are for x86, which has KVM_INTERNAL_MEM_SLOTS
> defined as 3.
>
> As far as I can see aarch64 has KVM_INTERNAL_MEM_SLOTS equal to 0, so
> this arch has 32766 slot available for the test memory.
>
> Quick calculations show that this will result in 112 KiB of memory in
> the last slot for 4 KiB page size (while for 64 KiB page size the
> maximum slot count for this test is 8192 anyway - not counting slot 0).
>
It seems your calculation had (512MB+64KB), instead of (512MB+4KB).
In this particular patch, we still have (512MB+4KB). How about to change
like below in this patch. In next patch, it's adjusted accordingly after
we have (512MB+64KB).
(1) In this patch, the comment is changed to as below
/*
* We have different number of memory slots, excluding the reserved
* memory slot 0, on various architectures and configurations. The
* memory size in this test is calculated by doubling the maximal
* memory size in last memory slot, with alignment to the largest
* supported page size (64KB).
*
* architecture slots memory-per-slot memory-on-last-slot
* --------------------------------------------------------------
* x86-4KB 32763 16KB 100KB
* arm64-4KB 32766 16KB 52KB
* arm64-64KB 8192 64KB 64KB
*/
#define MEM_TEST_MOVE_SIZE 0x40000 /* 256KB */
(2) In the next patch, where we have (512MB+64KB) after the various
memory sizes are consolidated, It is adjusted accordingly as below.
/*
* We have different number of memory slots, excluding the reserved
* memory slot 0, on various architectures and configurations. The
* memory size in this test is calculated by doubling the maximal
* memory size in last memory slot, with alignment to the largest
* supported page size (64KB).
*
* architecture slots memory-per-slot memory-on-last-slot
* --------------------------------------------------------------
* x86-4KB 32763 16KB 160KB
* arm64-4KB 32766 16KB 112KB
* arm64-64KB 8192 64KB 128KB
*/
#define MEM_TEST_MOVE_SIZE 0x50000 /* 320KB */
Thanks,
Gavin
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