[haiku-bugs] Re: [Haiku] #9019: add iotop utility

  • From: "anevilyak" <trac@xxxxxxxxxxxx>
  • Date: Sun, 23 Sep 2012 20:44:37 -0000

#9019: add iotop utility
   Reporter:  Prasad                           |      Owner:  nobody
       Type:  enhancement                      |     Status:  new
   Priority:  normal                           |  Milestone:  R1
  Component:  Applications/Command Line Tools  |    Version:
 Resolution:                                   |  R1/Development
 Blocked By:                                   |   Keywords:
Has a Patch:  1                                |   Blocking:
                                               |   Platform:  All

Comment (by anevilyak):

 Replying to [comment:5 Prasad]:
 > Accounting for IOs can be performed at various levels, for example:
 read, write system calls or, as you pointed out, when a an IO is submitted
 to the device.

 The syscalls can't really report accurate/meaningful stats though, as
 they're completely unaware of a) any ancillary operations that are an
 indirect result of their particular request, and b) how many operations a
 given request actually resulted in. To illustrate, consider the case of
 creating/deleting files. The syscall layer has absolutely no idea as to
 how much I/O such an operation actually results in since that completely
 depends on what housekeeping metadata operations the underlying filesystem
 had to do. Likewise, writing to a file might well result in the filesystem
 having to allocate more blocks for it, which also incurs extra operations
 outside of the requested write. Furthermore, if the I/O scheduler batches
 reads/writes into a single call, the syscall interface wouldn't know that
 either. It also wouldn't be aware if the underlying filesystem/device is
 in fact a RAID or other form of distributed storage that resulted in
 duplicate I/O operations being dispatched to multiple devices. Given all
 these caveats, accounting via the syscall interface presents at best an
 incomplete picture, and at worst an outright misleading one, which renders
 it pretty much useless unless your only goal is to print some numbers.

Ticket URL: <http://dev.haiku-os.org/ticket/9019#comment:8>
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