Messages in this thread | | | Date | Sun, 12 Apr 2015 10:36:34 +0200 | From | Nicholas Mc Guire <> | Subject | Re: [PATCH 2/3] time: allow gcc to fold constants when using msecs_to_jiffies |
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> Your inline version has not worked with any of > x86-64 gcc 4.4, 4.6, 4.7, or 4.9 > > I suggest you add some lines to > lib/test_module.c/test_module_init like: > > unsigned int m; > > for (m = 10; m < 200; m += 10) > pr_info("msecs_to_jiffies(%u) is %lu\n", > m, msecs_to_jiffies(m)); > > pr_info("msecs_to_jiffies(%u) is %lu\n", > 10, msecs_to_jiffies(10)); > pr_info("msecs_to_jiffies(%u) is %lu\n", > 100, msecs_to_jiffies(100)); > pr_info("msecs_to_jiffies(%u) is %lu\n", > 1000, msecs_to_jiffies(1000)); > > Then it's pretty easy to look at the assembly/.lst file > > Your inline function doesn't allow gcc to precompute > the msecs_to_jiffies value. The macro one does for all > those gcc versions. > > Try it and look at the generated .lst files with and > without the patch I sent. > I have checked it with the testcase you proposed - and I quite sure it is working, find the .s file snippets from the test_module.c modified as you suggested below. HZ is set to 300 so that it is easy to differenciate the parameter to msecs_to_jiffies and the printed const.
there is no call and no calculation for the constant cases - just load as it should be.
with the patch applied: test_module_init: pushq %rbp # movq %rsp, %rbp #, pushq %rbx # movl $10, %ebx #, m pushq %rcx # .L4: movl %ebx, %edi # m, call __msecs_to_jiffies # movl %ebx, %esi # m, movq %rax, %rdx # D.14515, movq $.LC1, %rdi #, xorl %eax, %eax # addl $10, %ebx #, m call printk # cmpl $200, %ebx #, m jne .L4 #, <---end of for loop movl $3, %edx #, <---msecs_to_jiffies(10) movl $10, %esi #, movq $.LC1, %rdi #, xorl %eax, %eax # call printk # movl $30, %edx #, <---msecs_to_jiffies(100) movl $100, %esi #, movq $.LC1, %rdi #, xorl %eax, %eax # call printk # movl $300, %edx #, <---msecs_to_jiffies(1000) movl $1000, %esi #, movq $.LC1, %rdi #, xorl %eax, %eax # call printk #
without the patch applied:
pushq %rbp # movq %rsp, %rbp #, pushq %rbx # movl $10, %ebx #, m pushq %rcx # .L2: movl %ebx, %edi # m, call msecs_to_jiffies # movl %ebx, %esi # m, movq %rax, %rdx # D.14503, movq $.LC0, %rdi #, xorl %eax, %eax # addl $10, %ebx #, m call printk # cmpl $200, %ebx #, m jne .L2 #, movl $10, %edi #, call msecs_to_jiffies # movl $10, %esi #, movq %rax, %rdx # D.14504, movq $.LC0, %rdi #, xorl %eax, %eax # call printk # movl $100, %edi #, call msecs_to_jiffies # movl $100, %esi #, movq %rax, %rdx # D.14505, movq $.LC0, %rdi #, xorl %eax, %eax # call printk # movl $1000, %edi #,
could you check the .s file for you test module ? I'm a bit lost on why you are not seeing this - also checked with cross-build (multi_v7_defconfig) and it looks like thats working as well.
thx! hofrat
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