Q: after updating my iphone 4s 8gb to ios 8....icannot find personal hotspot option in settings app suggest me solution..

Only from Apple supported carriers

iOS: Understanding Personal Hotspot

iOS: Troubleshooting Personal Hotspot

iPhone: Wireless carrier support and features

I have upgraded my iPhone 4S 8GB to IOS 8.1 (12B411).

Personal Hotspot option is available in SETTINGS below Cellular option.

If Hotspot option is visible in your phone, however if it is disabled, then check your cellular/data connection.

Without cellular/data connection, you can not enable Personal Hotspot option.