To Developers: Way to improve ADC performance

In any ADC devices or networking appliances, there exists a data that will be accessed very often like session table, routing table, shared memory for IPC communications. In case of ADC, its cached objects, signature files for WAN optimization etc., Depending on the size, these memory entities will spawn in multiple pages. When ever there is a context switch, CPU needs to load these pages and that involves TLB lookup and cache lookup.

TLB(A translation lookaside buffer) is a CPU cache used to improve virtual address to physical address mapping.A TLB has a fixed number of slots that contain page table entries, which map virtual addresses to physical addresses. And,number of TLB entries are very few. If the requested address is present in the TLB, its a TLB hit and If the requested address is not in the TLB, the translation proceeds by looking up the page table in a process called a page walk. The page walk is an expensive process, as it involves reading the contents of multiple memory locations and using them to compute the physical address. After the physical address is determined, the virtual address to physical address mapping is entered into TLB.

Less number of TLB misses will give good performance. Since, session tables, routing tables, cached objects will be contiguous, using that fact if one TLB entry is allotted for such contiguous memory need for more TLB entries can be avoided. Each TLB entry mapping to huge chunks of contiguous memory is made possible by "hugetlbfs"

Allocate the session table, routing table, cached object memory from this hugetlfs and CPU performance is improved greatly as it conserves TLB entries and avoids costly page walk.
You can check this link to see how MySql was benefited with hugetlfs.

You can go through this linux documentation for implementation details and for more information.

References:
http://netsecinfo.blogspot.com

TLB wikipedia