cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 
ngreve
Visitor
Visitor
611 Views
Registered: ‎12-19-2018

Calculating PCIe Bandwith - WP350

Jump to solution

Currently I am trying to take a deeper look into the inner workings of PCIe.

I've found your whitepaper on "Understanding Performance of PCI Express Systems (WP350 (v1.2))".

In the Chapter "Symbol Encoding" on page 2 it is explained what the 8b10b encoding is, and that this symbol encoding is the cause of 20% loss of throughput. So far, so good...

In Chapter "Write Transaction Throughput" on page 12 an example calculation is done for the throughput of 200 write transactions (Example 1). But what I am missing in this calculation is the consideration of the 8b10b encoding. Shouldn't there be a 20% addition somewhere in Step 4, caused by the used encoding, or am I missing something?

 

0 Kudos
1 Solution

Accepted Solutions
aforencich
Explorer
Explorer
468 Views
Registered: ‎08-14-2013

It's considered in the byte transfer time of 4 ns.  The raw bit rate is 2.5 GT/s after 8b/10b encoding.  Before 8b/10b encoding, it is 2 Gb/s (see table 2).  It takes 8 bits / 2 Gb/s = 4 ns to transfer each byte. 

View solution in original post

2 Replies
aforencich
Explorer
Explorer
469 Views
Registered: ‎08-14-2013

It's considered in the byte transfer time of 4 ns.  The raw bit rate is 2.5 GT/s after 8b/10b encoding.  Before 8b/10b encoding, it is 2 Gb/s (see table 2).  It takes 8 bits / 2 Gb/s = 4 ns to transfer each byte. 

View solution in original post

ngreve
Visitor
Visitor
458 Views
Registered: ‎12-19-2018
I really don't know how i missed that (multiple times). Thanks!
0 Kudos