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Date: Sat, 13 Mar 2021 09:00:12 +0900 From: Daeho Jeong <daeho43@...il.com> To: Greg KH <gregkh@...uxfoundation.org> Cc: linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com, Daeho Jeong <daehojeong@...gle.com> Subject: Re: [PATCH v4] f2fs: add sysfs nodes to get runtime compression stat 2021년 3월 12일 (금) 오후 11:45, Greg KH <gregkh@...uxfoundation.org>님이 작성: > > A: http://en.wikipedia.org/wiki/Top_post > Q: Were do I find info about this thing called top-posting? > A: Because it messes up the order in which people normally read text. > Q: Why is top-posting such a bad thing? > A: Top-posting. > Q: What is the most annoying thing in e-mail? > > A: No. > Q: Should I include quotations after my reply? > > http://daringfireball.net/2007/07/on_top > Thanks for letting me know this! > > On Fri, Mar 12, 2021 at 11:37:29PM +0900, Daeho Jeong wrote: > > As you can see, if we're doing like the below. > > > > sbi->compr_written_block += blocks; > > > > Let's assume the initial value as 0. > > > > <thread A> <thread B> > > sbi->compr_written_block = 0; > > > > sbi->compr_written_block = 0; > > +blocks(3); > > + blocks(2); > > sbi->compr_written_block = 3; > > > > sbi->compr_written_block = 2; > > > > Finally, we end up with 2, not 5. > > > > As more threads are participating it, we might miss more counting. > > Are you sure? Isn't adding a number something that should happen in a > "safe" way? > > And if you miss 2 blocks, who cares? What is so critical about these > things that you take the cache flush of 2 atomic writes just for a > debugging statistic? > > Why not just take 1 lock for everything if it's so important to get > these "correct"? > > What is the performance throughput degradation of adding 2 atomic writes > to each time you write a block? > > But really, will you ever notice missing a few, even if that could be > possible on your cpu (and I strongly doubt most modern cpus will miss > this...) > > But this isn't my code, I just hate seeing atomic variables used for > silly things like debugging stats when they do not seem to be really > needed. So if you want to keep them, go ahead, but realize that the > number you are reading has nothing to do with being "atomic" at all. > > thanks, > I agree that missing number would be extremely few and the overhead of updating the numbers would be quite bad. Thanks for your valuable comments. :) > greg k-h
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