Hi Catalin,
On 6/3/19 10:21 PM, Catalin Marinas wrote:
On Mon, Jun 03, 2019 at 05:25:34PM +0100, Catalin Marinas wrote:
On Tue, May 21, 2019 at 06:21:39PM +0100, Julien Grall wrote:
Since a softirq is supposed to check may_use_simd() anyway before
attempting to use FPSIMD/SVE, there is limited reason to keep softirq
disabled when touching the FPSIMD/SVE context. Instead, we can simply
disable preemption and mark the FPSIMD/SVE context as in use by setting
CPU's fpsimd_context_busy flag.
[...]
+static void get_cpu_fpsimd_context(void)
+{
+ preempt_disable();
+ __get_cpu_fpsimd_context();
+}
Is there anything that prevents a softirq being invoked between
preempt_disable() and __get_cpu_fpsimd_context()?
Actually, it shouldn't matter as the softirq finishes using the fpsimd
before the thread is resumed.
If the softirqs is handled in a thread (i.e ksoftirqd), then
preempt_disable() will prevent them to run.
For softirq running on return from interrupt context, they will finish
before using fpsimd before the thread is resumed.
Softirq running after __get_cpu_fpsimd_context() is called will not be
able to use FPSIMD (may_use_simd() returns false).
Cheers,
--
Julien Grall
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