On Thu, Mar 23, 2023 at 06:22:55AM +0100, Greg KH wrote: > On Thu, Mar 23, 2023 at 10:35:59AM +0530, Deepak R Varma wrote: > > On Thu, Mar 23, 2023 at 05:58:02AM +0100, Greg KH wrote: > > > Nice, that shows that it is the same both ways as the compiler version > > > you are using is smart enough > > > > > > Which compiler and version is this? Does it work the same for all of > > > the supported versions we have to support (i.e. really old gcc?) > > > > > > For the most part, sysfs files are not on any sort of "fast path" so a > > > > Hello, > > Is there a guideline/documentation on how to identify if a code is part of > > fast/slow path? > > Not really, the general rule is if the code is used in a function that > is time criticial, then it is in the "fast path". > > Normally the code path for I/O or for determining what process to > schedule next is a "fast path" as you want to do the least amount of > work in the kernel so as to get the I/O to the hardware or caller, or > you want to schedule the next process faster so that it can do the real > work that is wanted. > > But for some I/O, where the hardware is the limiting factor (like slow > USB or serial connections), no matter how optimized the kernel is, the > data can not get to the user any faster because the hardware just can > not provide it, so for that, it's not really that critical. > > Note that "time critical" can change depending on the user of the system > and as hardware evolves. > > One example would be the creation of a number of sysfs entries for the > disks in the systems. On a "normal" system, creating them all is trivial > as there are not many disks. But on some "big" systems with many tens > of thousands of disks, it can become a boot time bottleneck. > > So it's usually "you know it when you see it show up on a profile", use > the perf tool to test your workload on, to see where in the kernel > things are taking up too much time so you know what needs to be made > faster. > > hope this helps, Thank you Greg. Yes, it definitely is very helpful. I sincerely appreciate the explanation and the time you took to write it in so detail. I am Obliged. Regards, Deepak. > > greg k-h
