wotlk pvp dks haste

i play on 2-3 servers, so keep the discussion blizzlike please

is it supposed to lower our GCD on spells? if yes does it also work with unholy presence as if lowering the GCD to 0,9 0,8 etc?

any info is appreciated

Any ability classified as a spell (Death Coil, Pestilence, Blood Boil, etc.) will have the GCD it inflicts upon the caster reduced by haste up to 1s GCD. Haste does not affect abilities that are not considered spells (Scourge Strike, Frost Strike, Plague Strike, Blood Strike, etc.). Unholy presence works for both type of abilities with the same restriction of not being able to lower your GCD below 1s.