ith dwindling game support and
expensive hardware requirements, is
it still worth setting up an SLI system?
Tofindout,we enlisted Scan (scan.co.uk), which
kindly loaned us a top-end SLI rig for testing.
Carefully built inside a smart and subtle NZXT
H710 case, the Scan test rig features a Ryzen 9
3950X CPU cooled by a Corsair all-in-one liquid
cooler with a 360mm radiator in the front.
It also comes with a 2TB PCI-E 4 SSD and
a pair of EVGA GeForce RTX 2080 Ti graphics
cards with a light-up EVGA NVLink connector.
In addition, Scan sent us a pair of EVGA GeForce
RTX 2080 Super cards, so we could test two SLI
configurations. It all plugs into an Asus ROG Strix
X570 motherboard, which has an SLI-friendly
design, putting a slot space between the two
dual-slot graphics cards, giving them a bit of
space to breathe. It’s a good-looking machine,
withwell-tidiedcablesandsmartlighting.
Problems
It’sfairtosaythatourexperiencewithSLI
wasn’tentirelysmoothfromtheoutset.Thefirst
issuewespottedwasthatNvidiaFrameView
wasn’tproperlyrecordingtheframerates,
whichis a littleironic,giventhatbothFrameView
and SLI are Nvidia technologies. Basically, the
frame rates reported in FrameView in DirectX
were significantly lower than the frame rates
reported by FRAPS and in-game frame rate
counters. You could also visibly see that the
FrameView results were incorrect – some
games were running smoothly, while
FrameView was reporting results that should
have meant they were unplayable.
As a result, we’ve had to go back to reporting
the minimum and average for this test, rather
than the 99th percentile, for DirectX games.
FrameView still worked fine in Vulkan, though,
so we’ve reported 99th percentile results for
our Red Dead Redemption 2 test.
The other problem we had was that not all of
our usual test games support SLI as standard.
Our standard ray-tracing test game, Battlefield
V, is restricted to single-GPU rendering. In the
past,therewerewaysaroundthisproblem,as
withothergames,bymakinga customprofile.
ProfileInspectoris downloadablefrom
nvidiaprofileinspector.com, andenablesyou
toforcesomegameexecutablestousea
customSLIprofile– this sometimesimproves
performanceoverthedefaultprofile,and
canalsoforcegameslimitedtooneGPUto
usetwoGPUs.If youhaveanSLIsetup,it’s
worthGooglingtoseehowotherpeoplehave
optimisedtheirgameswithcustomprofiles.
InBattlefieldV,youusedtobeabletosetit to
use the Battlefield 4 SLI profile and then force
it to use AFR. However, a later patch for the
game knocked this on the head. You can still get
it working in SLI if you’re prepared to do a lot of
faffing, which also involves disabling several
graphical settings, but for this feature we instead
decided to concentrate on games that could
run with SLI out of the box, so we’ve tested ray
tracing with the ray-traced shadows feature in
Shadow of the Tomb Raider.Likewise,UnigineSuperposition,whichwe
usuallyusetotestloadpowerconsumption,
alsodoesn’tworkwithSLI,sowe’veinstead
testedloadpowerconsumptionwithShadow
oftheTombRaider.
Asweexpected,SLIperformanceis variable
acrosstitles,butthescalingyoucanexpectalso
varies wildly between cards and resolutions.
In several of our games, we saw better scaling
from our pair of RTX 2080 Supers than the RTX
2080 Tis, and vice versa.
This makes it hard to make claims for
any hard and fast rules. In theory, you
might expect SLI scaling to be better at one
resolution than another, but it also depends
on the drivers and compatibility issues. For
example, Shadow of the Tomb Raider at 4KPERFORMANCE
ANALYSIS
Scan sent us an air-cooled SLI rig for testing,
although most of its customers sensibly prefer their
SLI gear to be water-cooledThere’s a slot space between the two EVGA RTX
2080 Ti cards, so they can breathe
W