Re: Is Parallel Programming Hard, And, If So, What Can You Do About It?

On 5/12/2025 8:03 PM, Lawrence D'Oliveiro wrote:

On Mon, 12 May 2025 21:50:02 -0400, Stefan Monnier wrote:
 

But the drive also knows things about the data that the OS can't know
(things that have to do with the physical location of the data on the
platters).

 No it doesn’t. Consider a journalling filesystem, where the journal entry
must be written first before the actual filesystem update. If the drive
reorders the writes to do the latter first, there go your filesystem
integrity guarantees.

First of all, you said that there aren't things that the drive knows but the host doesn't.  This isn't true (e.g. which disk sectors are defective and had to be relocated), and the rest of your response doesn't refute that, but talks about file system stuff.  Secondly, if a particular write, in your example, the journal write has to be completed before the other write, the disk provides that capability.  It has nothing to do with what the disk knows.
--
  - Stephen Fuld
(e-mail address disguised to prevent spam)