Questions RE: /proc/stat

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Dear list,

I had some questions regarding using /proc/stat (on the 2.6 kernel).

Can I assume that reading /proc/stat is 'atomic'? Can I assume that when I read

the file, that nothing will change the data while I am reading it?
IE:
  cpu  15948315 4687107 3321012 122412279 659908 43304 144288
  cpu0 15948315 4687107 3321012 122412279 659908 43304 144288

can I assume that while I am reading the third value (system), that the fourth value (idle) will not be changed underneath me? Can I assume that all the lines? cpu, cpu0 will all be

generated at once?


My second question is regarding using these values to calculate usage...

Should I calculate usage by
(where T1, T2 are time)

A) read /proc/stat

Fill variables UserT1, NiceT1, SystemT1, IdleT1, IOWaitT1, irqT1, irq2T1

   wait a time

Fill variables UserT2, NiceT2, SystemT2, IdleT2, IOWaitT2, irqT2, irq2T2 DeltaTotalTime=(UserT2-UserT1)+(NiceT2-NiceT1)+(SystemT2-SystemT1) +(.........)

Then calculate the values I want as the delta variableOfInterest / total delta

   ie: (UserT2-UserT1)/DeltaTotalTime

Can I assume that all these values added together should add up to 100%?

or


B) read /proc/stat
   read variable of interest, ie: UserT1 and btimeT1 and number of CPUs
   wait a time
   read variable of interest, ie: UserT2 and btimeT2 and number of CPUs

   Then calculate the values I want as
     ((UserT2-UserT1)/NumCPU)/(btimeT2-btimeT1)*100 (Jiffies)



Thanks for any comments

Regards

Andrew



-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.1 (Darwin)

iD8DBQFDkGWSW126qUNSzvURAhdrAJ9bmadzIAZfzMZ83PmuWZ2e67OW9wCfbcU2
SO3Do1kRaxy+4LRhyL9y/9s=
=r+rR
-----END PGP SIGNATURE-----
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

---

• Follow-Ups:
  • /proc/stat [Subject changed]
    • From: Andrew Miehs <[email protected]>

• Prev by Date: Re: [PATCH 02/12] mm: supporting variables and functions for balanced zone aging
• Next by Date: Re: [q] make modules_install as non-root?
• Previous by thread: SNA NETWORK LAYER
• Next by thread: /proc/stat [Subject changed]
• Index(es):
  • Date
  • Thread

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]