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SubjectRe: New Benchmark tools, lookie looky........
Larry McVoy writes:
> On Tue, Oct 17, 2000 at 09:21:00AM -0700, Andre Hedrick wrote:
> > Expand 'traces' ... O-SCOPE analyizer?
> Insert a ring buffer into the disk sort entry point. Add a userland process
> which reads this ring buffer and gets the actual requests in the actual order
> they are sent to the drive[s]. Then take that data and write a simulator into
> which you can plug in different algs. I have all this crud for SunOS if you
> want it, including elevator.c, hacksaw.c, and inorder.c.

I wrote a lightweight kernel->userland ring buffer device for Linux
called bufflink and a block-request logger that uses it called
reqlog. reqlog writes a structure
struct reqlog {
unsigned int major;
unsigned int minor;
unsigned long sector;
long nr_sectors;
to the ring buffer when an ioctl is done to enable logging. The
current patch isn't quite what you were suggesting since it does

add_request() {
elevator_queue(req, tmp, latency, dev, current_request);
+ if (bl_reqlog && enable_reqlog) {
+ ...
+ bufflink_append(bl_reqlog, (unsigned char *)&rl, sizeof rl);
+ }

if (queue_new_request)
but it would be easy to write the record (instead or as well)
before the elevator_queue(). The patches are available from


Malcolm Beattie <>
Unix Systems Programmer
Oxford University Computing Services
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