> The counts are off by one.
>
> With a UP kernel, I see that fget() cost is negligible.
> So it is most likely the atomic operations for rwlock acquisition/release
> in fget() that is adding to its cost. Unless of course my sampling
> is too less.
Mine is a UP box not an SMP kernel, although preempt is enabled;
0xc013d370 <fget>: push %ebx
0xc013d371 <fget+1>: mov %eax,%ecx
0xc013d373 <fget+3>: mov $0xffffe000,%edx
0xc013d378 <fget+8>: and %esp,%edx
0xc013d37a <fget+10>: incl 0x4(%edx)
0xc013d37d <fget+13>: xor %ebx,%ebx
0xc013d37f <fget+15>: mov 0x554(%edx),%eax
0xc013d385 <fget+21>: cmp 0x8(%eax),%ecx
0xc013d388 <fget+24>: jae 0xc013d390 <fget+32>
0xc013d38a <fget+26>: mov 0x14(%eax),%eax
0xc013d38d <fget+29>: mov (%eax,%ecx,4),%ebx
0xc013d390 <fget+32>: test %ebx,%ebx
0xc013d392 <fget+34>: je 0xc013d397 <fget+39>
0xc013d394 <fget+36>: incl 0x14(%ebx)
0xc013d397 <fget+39>: decl 0x4(%edx)
0xc013d39a <fget+42>: mov 0x14(%edx),%eax
0xc013d39d <fget+45>: cmp %eax,0x4(%edx)
0xc013d3a0 <fget+48>: jge 0xc013d3a7 <fget+55>
0xc013d3a2 <fget+50>: call 0xc01179b0 <preempt_schedule>
0xc013d3a7 <fget+55>: mov %ebx,%eax
0xc013d3a9 <fget+57>: pop %ebx
0xc013d3aa <fget+58>: ret
0xc013d3ab <fget+59>: nop
0xc013d3ac <fget+60>: lea 0x0(%esi,1),%esi
> Please try running the files_struct_rcu patch where fget() is lockfree
> and let me know what you see.
Lock acquisition/release should be painless on this system no?
Zwane
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