Is there any way to reduce render time on volumetric (Fire, smoke ..), with Mantra?

You should describe a bit the scene you made. How many lights, what type of shadows, what renderer? And more importantly what's the effect you're having issues with.

Thanks,
for example I want to make a demo-real with exploding ground, breaking dusts, smokes, fires.
Also I tested with simple scene, which include a sphere with fire fluid on it and I rendered for example frame 20, with 640x480, but it really take long time to render, my cpu is intel 2-due-core-E6750, my previous work on Maya's fluid, it took around 1-2 min to render (MR or Maya render), also I tested with 3delight in Maya and it is not bad, but with Great fluid in Houdini, for ordinary cpu is realy takes time to render, though.
May be some tricks there that I don't know.

2 quickies:

- use deep shadowmaps
- increase Mantra->Sampling->Volume Step Size

Shylon
my cpu is intel 2-due-core-E6750

This is really very very outdated cpu. Don't expect acceptable render times with this 6 years old cpu.

Yes my CPU is seems old, but the tricks that “eetu” wrote, really worked and amount of time reduced.
Thanks. :?

You can also make 2 Mantra ROP, one only for volumetric with force matte geometry, another one without volumetric.