Messages in this thread | | | Date | Fri, 22 Apr 2011 10:08:59 -0700 | From | Sunil Mushran <> | Subject | Re: [PATCH 1/2] fs: add SEEK_HOLE and SEEK_DATA flags |
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On 04/22/2011 10:03 AM, Eric Blake wrote: >> cp can read whatever blocksize it chooses. If that block contains >> zero, it would signal cp that maybe it should SEEK_DATA and skip >> reading all those blocks. That's all. We are not trying to achieve >> perfection. We are just trying to reduce cpu waste. >> >> If the fs supports SEEK_*, then great. If it does not, then it is no >> worse than before. > But providing just SEEK_DATA _is_ worse than before if you don't provide > the correct SEEK_HOLE everywhere. Because then your algorithm of trying > lseek(SEEK_DATA) after every run of zeros in the hopes of an > optimization is a wasted syscall, since it will just return your current > offset every time, so you end up with more syscalls than if you had used > the single lseek(SEEK_DATA) that returns the end of the file up front, > and known that the remainder of the file has no holes to even try > seeking past.
You are over-optimizing. strace any process on your box and you will find numerous wasted syscalls.
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