RT patch for centos 8.1.1911

Hello,

I installed a customized kernel for centos 8.1.1911
The change I did: CONFIG_CMA=y

Now I have to add the RT patch.
I downloaded: patch-4.18.16-rt9.patch.xz and then:
cd linux-4.18.0-147
xzcat ../patch-4.4.12-rt19.patch.xz | patch -p1

I got the output listed in the attached patch.txt

It seems that the patch process ended with few errors.
for example:
Hunk #1 FAILED at 38.
...
Hunk #8 FAILED at 2110.
Hunk #9 FAILED at 2130

Can you please explain the reason for those errors ?
Is it the right way to patch this kernel ?

Thank you,
Zvika