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fbcyborg
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PostPosted: Thu Dec 02, 2010 9:25 am    Post subject: Kernel aggiornato problemi con MTRR Reply with quote

Salve a tutti,

ho aggiornato di recente il kernel dalla versione 2.6.35-gentoo-r11 alla versione 2.6.36-gentoo-r3 e al boot da quando faccio partire l'ultimo kernel vedo questa serie di messaggi.
Code:
mtrr: type mismatch for fb000000,800000 old: write-back new: write-combining
mtrr: type mismatch for fb000000,400000 old: write-back new: write-combining
mtrr: type mismatch for fb000000,200000 old: write-back new: write-combining
mtrr: type mismatch for fb000000,100000 old: write-back new: write-combining
mtrr: type mismatch for fb000000,80000 old: write-back new: write-combining
mtrr: type mismatch for fb000000,40000 old: write-back new: write-combining
mtrr: type mismatch for fb000000,20000 old: write-back new: write-combining
mtrr: type mismatch for fb000000,10000 old: write-back new: write-combining
mtrr: type mismatch for fb000000,8000 old: write-back new: write-combining
mtrr: type mismatch for fb000000,4000 old: write-back new: write-combining
mtrr: type mismatch for fb000000,2000 old: write-back new: write-combining
mtrr: type mismatch for fb000000,1000 old: write-back new: write-combining

In realtà questo problema l'ho (diciamo) risolto, ma mi restano alcuni dubbi. Cercando in giro, sempre per il forum, ho scoperto che la causa era un parametro nel grub.conf che non era corretto: mtrr:3. Ho quindi settato mtrr:2, e questi messaggi non compaiono più, ma compare quanto segue (è anche indentato molto rispetto ai soliti messaggi di boot):
Code:
msgmni has been set to 7915
io scheduler noop registered
io scheduler deadline registered (default)
lp: driver loaded but no devices found
Real Time Clock Driver v1.12b
Linux agpgart interface v0.103
uvesafb: NVIDIA Corporation, BIOS-P/N@N4273:0, Chip Rev   , OEM: NVIDIA, VBE v3.0
uvesafb: VBIOS/hardware doesn't support DDC transfers
uvesafb: no monitor limits have been set, default refresh rate will be used
uvesafb: scrolling: redraw
Console: switching to colour frame buffer device 160x64
uvesafb: framebuffer at 0xfb000000, mapped to 0xffffc90000080000, using 13781k, total 14336k

Il che sembra tutto OK.

Ora vorrei capire innanzitutto perché con il precedente kernel non si presentava questo problema, e soprattutto cosa mi cambia all'atto pratico passare da 3 a 2.
Ho già letto questo wiki, oltre alla documentazione in /usr/src/linux/Documentation/x86/mtrr.txt, ed ho visto che, per quanto riguarda i valori per mtrr abbiamo:
Code:
0 - Disabled (equivalent to nomtrr) (default)
1 - Uncacheable
2 - Write-back
3 - Write-combining
4 - Write-through

Il valore ottimale è 3. Perché non posso più usare il valore ottimale?
La differenza fra i concetti write-back, write throug la conosco.
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