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Message-ID: <bb1c22ef-8cdb-2fc8-5ff7-f6cd92bf935d@huawei.com>
Date: Mon, 21 Nov 2022 21:38:12 +0800
From: chenlifu <chenlifu@...wei.com>
To: Andrew Jones <ajones@...tanamicro.com>
CC: <anup@...infault.org>, <atishp@...shpatra.org>,
<paul.walmsley@...ive.com>, <palmer@...belt.com>,
<aou@...s.berkeley.edu>, <kvm@...r.kernel.org>,
<kvm-riscv@...ts.infradead.org>, <linux-riscv@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] RISC-V: KVM: optimize kvm_arch_hardware_enable()
在 2022/11/21 18:53, Andrew Jones 写道:
> On Mon, Nov 21, 2022 at 08:39:15AM +0800, Chen Lifu wrote:
>> The values of CSR_HEDELEG and CSR_HIDELEG registers are constants,
>> so change them from variables to macros.
>>
>> Signed-off-by: Chen Lifu <chenlifu@...wei.com>
>> ---
>> arch/riscv/kvm/main.c | 31 +++++++++++++------------------
>> 1 file changed, 13 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/riscv/kvm/main.c b/arch/riscv/kvm/main.c
>> index df2d8716851f..70196b03b6f9 100644
>> --- a/arch/riscv/kvm/main.c
>> +++ b/arch/riscv/kvm/main.c
>> @@ -12,10 +12,21 @@
>> #include <linux/kvm_host.h>
>> #include <asm/csr.h>
>> #include <asm/hwcap.h>
>> #include <asm/sbi.h>
>>
>> +#define EXC_HEDELEG ((1UL << EXC_INST_MISALIGNED) | \
>> + (1UL << EXC_BREAKPOINT) | \
>> + (1UL << EXC_SYSCALL) | \
>> + (1UL << EXC_INST_PAGE_FAULT) | \
>> + (1UL << EXC_LOAD_PAGE_FAULT) | \
>> + (1UL << EXC_STORE_PAGE_FAULT))
>> +
>> +#define IRQ_HIDELEG ((1UL << IRQ_VS_SOFT) | \
>> + (1UL << IRQ_VS_TIMER) | \
>> + (1UL << IRQ_VS_EXT))
>> +
>> long kvm_arch_dev_ioctl(struct file *filp,
>> unsigned int ioctl, unsigned long arg)
>> {
>> return -EINVAL;
>> }
>> @@ -30,29 +41,13 @@ int kvm_arch_hardware_setup(void *opaque)
>> return 0;
>> }
>>
>> int kvm_arch_hardware_enable(void)
>> {
>> - unsigned long hideleg, hedeleg;
>> -
>> - hedeleg = 0;
>> - hedeleg |= (1UL << EXC_INST_MISALIGNED);
>> - hedeleg |= (1UL << EXC_BREAKPOINT);
>> - hedeleg |= (1UL << EXC_SYSCALL);
>> - hedeleg |= (1UL << EXC_INST_PAGE_FAULT);
>> - hedeleg |= (1UL << EXC_LOAD_PAGE_FAULT);
>> - hedeleg |= (1UL << EXC_STORE_PAGE_FAULT);
>> - csr_write(CSR_HEDELEG, hedeleg);
>> -
>> - hideleg = 0;
>> - hideleg |= (1UL << IRQ_VS_SOFT);
>> - hideleg |= (1UL << IRQ_VS_TIMER);
>> - hideleg |= (1UL << IRQ_VS_EXT);
>> - csr_write(CSR_HIDELEG, hideleg);
>> -
>> + csr_write(CSR_HEDELEG, EXC_HEDELEG);
>> + csr_write(CSR_HIDELEG, IRQ_HIDELEG);
>> csr_write(CSR_HCOUNTEREN, -1UL);
>> -
>> csr_write(CSR_HVIP, 0);
>>
>> return 0;
>> }
>>
>> --
>> 2.37.1
>>
>
> I don't think this optimizes anything. I'm pretty sure the compiler will
> load the input to csr_write() in the most efficient way it can, regardless
> of using a constant or building the input out of constants. This could
> maybe be considered a code cleanup, but, in this case, it's really in the
> eye of the beholder.
>
> Thanks,
> drew
Thanks drew,you're right.
I compared two version arch/riscv/kvm/main.o files, they are same.
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