Re: "Enhanced" MD code avaible for review

From: Justin T. Gibbs
Date: Tue Mar 30 2004 - 17:17:49 EST

>> So you are saying that this presents an unrecoverable situation?
> No, I'm saying that the data phase need not have a bunch of in-kernel
> checks, it should be generated correctly from the source.

The SCSI drivers validate the controller's data phase based on the
expected phase presented to them from an upper layer. I never talked
about adding checks that make little sense or are overly expensive. You
seem to equate validation with huge expense. That is just not the
general case.

>> Hmm. I've never had someone tell me that my SCSI drivers are slow.
> This would be noticed in the CPU utilization area. Your drivers are
> probably a long way from being CPU-bound.

I very much doubt that. There are perhaps four or five tests in the
I/O path where some value already in a cache line that has to be accessed
anyway is compared against a constant. We're talking about something
down in the noise of any type of profiling you could perform. As I said,
validation makes sense where there is basically no-cost to do it.

>> I don't think that your statement is true in the general case. My
>> belief is that validation should occur where it is cheap and efficient
>> to do so. More expensive checks should be pushed into diagnostic code
>> that is disabled by default, but the code *should be there*. In any event,
>> for RAID meta-data, we're talking about code that is *not* in the common
>> or time critical path of the kernel. A few dozen lines of validation code
>> there has almost no impact on the size of the kernel and yields huge
>> benefits for debugging and maintaining the code. This is even more
>> the case in Linux the end user is often your test lab.
> It doesn't scale terribly well, because the checks themselves become a
> source of bugs.

So now the complaint is that validation code is somehow harder to write
and maintain than the rest of the code?


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at