On 7/11/2023 6:25 PM, Will Deacon wrote:
On Tue, Jul 11, 2023 at 06:15:49PM +0800, Aiqun(Maria) Yu wrote:
On 7/11/2023 4:22 PM, Will Deacon wrote:
On Tue, Jul 11, 2023 at 12:02:22PM +0800, Aiqun(Maria) Yu wrote:
On 7/10/2023 5:37 PM, Will Deacon wrote:
On Mon, Jul 10, 2023 at 01:59:55PM +0800, Maria Yu wrote:
In order to be able to disable lse_atomic even if cpu
support it, most likely because of memory controller
cannot deal with the lse atomic instructions, use a
new idreg override to deal with it.
This should not be a problem for cacheable memory though, right?
Given that Linux does not issue atomic operations to non-cacheable mappings,
I'm struggling to see why there's a problem here.
The lse atomic operation can be issued on non-cacheable mappings as well.
Even if it is cached data, with different CPUECTLR_EL1 setting, it can also
do far lse atomic operations.
Please can you point me to the place in the kernel sources where this
happens? The architecture doesn't guarantee that atomics to non-cacheable
mappings will work, see "B2.2.6 Possible implementation restrictions on
using atomic instructions". Linux, therefore, doesn't issue atomics
to non-cacheable memory.
We encounter the issue on third party kernel modules and third party apps
instead of linux kernel itself.
Great, so there's nothing to do in the kernel then!
The third party code needs to be modified not to use atomic instructions
with non-cacheable mappings. No need to involve us with that.
This is a tradeoff of performance and stability. Per my understanding,
options can be used to enable the lse_atomic to have the most performance
cared system, and disable the lse_atomic by stability cared most system.
Where do livelock and starvation fit in with "stability"? Disabling LSE
atomics for things like qspinlock and the scheduler just because of some
badly written third-party code isn't much of a tradeoff.
We also have requirement to have cpus/system fully support lse atomic
and cpus/system not fully support lse atomic with a generic kernel image.
Same kernel module wanted to be used by lse atomic fully support cpu and
not fully support cpu/system as well.
That's why we want to have a runtime option here.
Will
--
Thx and BRs,
Aiqun(Maria) Yu
