(cc dri-devel) On Mon, 20 Dec 2010 23:58:21 +0300 Michael Tokarev <mjt at tls.msk.ru> wrote:
> Hello. > > A weird problem here, and I'm looking for help in > an attempt to solve it. > > Ever since KMS went into kernel and I tried turning > it on, the scrolling speed on the resulting "text" > console (with kms it works in one of graphics modes > hence "text" in quotes) become really _awful_. > > For example, running `dmesg' (which has ~2000 lines) > on the console takes about 2.5 _minutes_ (!) to > complete, -- which means the speed is about 10 lines > per second. On an old notebook I have, with some also > nvidia card, the same operation completes in about > 0.8 sec. > > The lines goes up in a slow motion, I can watch every > new line appearing and scrolling. > > It was this way for a long time, and I almost gave up -- > in X everything works ok, and in order to speed up > booting again I just added "quiet" option to the kernel > command line, to avoid scrolling of kernel messages. > > But yesterday I noticed something else entirely, which > make me hope the problem actually _can_ be solved. > > The thing is: that same scrolling becomes much faster > when I "do something" else while it scrolls up. First > I noticed this when I wanted to switch to another vt > while it were scrolling -- I held down Ctrl key on my > keyboard, and out of the sudden the scroll speed up > dramatically. > > It turned out I can speed the thing to about 10 times > by generating some load: hit and hold a key on the > keyboard (generates interrupts?), run kernel compile > in the background (generates disk interrupts?), move > mouse... > > While doing "something", the same scrolling completes > in about 8 seconds instead of 2m30s. Dramatic improvement. > > Now, when I hold a key or move mouse, the scrolling > is "jumpy" - sometimes it slows down back to original > "slow" form for a bit, and sometimes it jumps a few > lines in one go. > > I tried to disable cpufreq (selecting "performance" > governor) - this changes exactly nothing. > > Next someone suggested the "perf" tool. And this one > is even more interesting: while `perf top' is running > (on another console or X), the scrolling is.. fast > again, as if I were moving my mouse! Once I stop > `perf top', it becomes slow again. So the bug > disappears while you watch it. > > And there I'm stuck again. I asked in #radeon, but > there, Alex Deucher told me that he has no clue and > that the behavour is weird (it is weird indeed). > > Any hints on where to go from there are apprecated. > > The hardware is an AMD780g-based motherboard with > and Athlon CPU, I've seen the same behavour from > many other similar boards. Kernels - all up to > the current 2.6.36.2, sine the old days when kms > for radeon first appeared in staging. > > I know kms/fbcon scrolling is slow on radeon because > it uses completely unoptimized bitblt routines (even > when the hw is pretty much capable of doing all that > stuff internally). But what I see here is something > different - the 8 sec to scroll 2000 lines is the > result from the un-optimal bitblt, not the 2m30s. > > Thanks! > > /mjt > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo at vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
